To let my step daughter call me "mum" ?

If your son was younger, I would maybe understand his argument, but he’s a grown man of 19 and he needs to get a grip.

@Lospecesenelrio you have clearly shown this child nothing but love and security and as a result she sees you as her Mum. That is a wonderful thing. Please do not give in and tell her she can not call you Mum, it would devastate her and cause damage to her confidence and the stability of your family. You sound like an amazing step mother!

Your son is 19 and needs to start acting like an adult.

OP please tell your DS to grow up.

In my extended family we have a little boy who was adopted. I saw him in Christmas day.. he's 8 now so nearly same age as your DD. he knows he's adopted. I was telling him how lovely the present his mum gave me.was and what a lovely person she is and he settled down next to me and said

" I've got 2 mums one who made me and one who loves me"

you may not have made your DSD but it certainly sounds like you love her. your DS needs to accept that there is plenty of love to go round and it takes nothing from him if she calls you mum because thats what you are un all but name anyway

I would have liked my own child's 'mum' & dad to have discussed this straight up when they planned to move in together given their actual mother was already out of the picture instead of conceiving now 4 year old twins.

This poor girl is probably searching for validation in her own family because the 'lets see what happens' & 'I'll treat every child the same (according to how i already raise my own children realistically)' didnt set proper guidelines when what should have happened when OP (already a mother to an older child herself) got with a man who had sole custody of barely out-pf-toddler-years child with no mother.... their should only ever have been a 'will I mother this child & have her taught what to call me so when shes comfortable she can switch' or 'I don't want this responsiblity'

I think it's lovely that she wants to call you Mum. Your DS is 19, not 9, and is being beyond childish. It's about time he grew up.

OP, have you ever talked to him in depth about the circumstances of you becoming pregnant at 15? Is he assuming it was a accident and you didn’t really want him? If that is part of his insecurity are you able to help him reframe that narrative to know he was loved and wanted, even if he (likely) wasn’t planned? If you’ve never sat down and explained how it happened that you came to have a baby at 15 he may have filled in the gaps with a very negative narrative. Basically is he worried you had him by accident but now you’re choosing to be a mother to a child who isn’t even related - you didn’t really want him but you do really want her.
Also you can reassure him that he doesn’t have to change how he refers to his step sister. She can still be his stepsister and the twins his half sisters if it’s important to him to explain that to people.
It sounds like it’s important for his sense of self to be transparent about his biological parenthood. But that doesn’t mean he can dictate how his stepsister defines her family and sense of self.

If your stepdaughter wants to call you mum you should absolutely let her. Your oldest son's feelings are misplaced. Parental love isn't a finite quantity that gets further divided with each child using that title.

But his feelings being misplaced doesn't mean they should be ignored entirely. It sounds like he did have a different childhood and family experience than your younger children are getting, and he might have all sorts of feelings of what-if or of being a bit on the outside of the family that are totally valid. Talk to him about the underlying feelings and look for ways to strengthen your relationship with him and his connection to the family as a whole. He's old enough for you to talk some about your own feelings as well.

You can do all of that while making it clear that your relationship with your stepdaughter (or twins) and your relationship with him are in no way mutually exclusive and that you won't tell her not to call you mum or permit unacceptable behavior in the home. In that respect it's similar to how you might handle a jealous older sibling when a new baby is born, just adapted for his age - don't tolerate bad behavior towards the new addition or you but have empathy for the older sibling's feelings and focus on reassuring them of their continued place in the family.

Your 19yo son is being a dick, quite frankly OP and needs to get over himself. How unkind of him. I’d be telling him exactly what I thought of his attitude and leave him to bloody well sulk if he must do. I think it’s absolutely beautiful that your SD wants to call you mum.

Is there no way to perhaps carefully broach with him trying to see things from her (SD's) perspective..?
I can't imagine how someone can be so callous and to be honest seemingly cruel if they've taken time to do that, so maybe he hasn't?

She's 9 right? and her mother hasn't been around for 4 years, so she was 5 years old when she came into your life.
Can he not even attempt to imagine what that must've been like for her??

5 is insanely young to be without your mother.
I get her mum made contact a handful of times, but honestly it's not surprise she's become attached to you in that way, and it's kind of bizarre to me that some posters think it's overstepping for her, by her own choice, to call you mum?

If SD's mother had god forbid passed away or given her up for adoption, or less extreme even let's say the lack of contact is booze related, would it still be unacceptable for her to start calling OP mum?

I'm a bit confused by the gatekeeping, she's 9, it's not like she's going to genuinely believe OP is her biological mum or that she's being made to believe her bio mum is some sort of fake mum - It just seems so odd to me to pander to the 19 year old in this scenario, why is he even bothered to begin with?

What does your husband call you?
maybe if he started calling you Mum or Ma?
I can understand him mot wanting to call your other half Dad as he has contact with his own dad but to get upset what someone else calls you is a bit entitled.
probably best to leave him to figure it out by himself.

He is being selfish but maybe his is jealous of the upbringing his siblings are having versus the one he has with you as you were so young?

Either way he needs to grow up and have empathy.

She's your daughter now. Let her call you mom.

I also would pick up on devonshiregal’s point that parental rejection hurts at any age. I would add to that that it is among the most visceral and difficult to process hurts that can be inflicted. If I’m perfectly honest, I’m in my 40’s but it would nonetheless take a little bit of processing for me even now if my mum were to announce that henceforth someone else was going to start calling her mum. If I were 19, barely out of childhood and hadn’t had that stability it would be a real issue for me. I think far too much of the strain and healing involved in blended families is heaped upon the children to process.

Agree with @Devonshiregal
also looking back now he may feel that he was not loved or treated in the same way when he was 0-9 years as the twins and DSD are now. That might be completely untrue but you say you were a teen mum, not in the same kind of stable couple. Instead of two parents he got one and lots of support from grandparents

He may be forgetting you being there when he was ill but is old enough now to see you do it for the others.

It doesn’t mean the behaviour is correct or should change that DSD calls you mum.

I feel this is crucial for her emotional well-being. It's an honour for a child to be so trusting and fond of you to want to call you mum. I say let her call you mum and re-iterate to your son the difference in ages, that it doesn't mean, couldn't mean, you love him less. Keep affirming and demonstrating your love for him, make time to do things together. To allow him to blackmail you into doing what he wants when it puts a little girl's health at risk isn't sending him a good message for his future relationships. Be gentle and patient with him while being firm about your decision. If he threatens anything more, you could say something like I can see this is affecting you deeply, and if you want to talk about it, I'm always here for you, but there can be no negotiation on my [your] decision, and no backlash on her. That's my take on it, but you must make the final decision.

I think you are a fantastic mother can I just say that. I also think the reason your son is acting this way is because your twins and his daughter all have a connection that he does not. I could be wrong but maybe he feels left out in a way.

YYY to all of this!
Op I think it is significant that he tells William about his issues with DSD and not you. I don't know why that is but again, there must be a reason and it's all interlinked. The more I read of this thread, the more convinced I feel therapy is the right thing here. Somehow communication has become an issue and you both need to work on it.

Not biologically, but in she has been married to her sub and for 7 years and SD is 9 she has been the stable maternal figure for the whole of SD’s memorable life. It sound like contact with the birth mother was sporadic and fizzled out at the age of 5.

The son is feeling insecure and jealous, but he is an adult. A mother and son counselling session may help to lay out the problem, firm up their bond, and help him to realise that DS is not a threat to him.

Please think about this deeply OP. This may well be the issue.. Don't try and logic him out of this or explain it away, emotions don't work that way and.he is entitled to feel how he feels. Whether how he feels is an accurate portrail or not he still feels that way. Everyone else in the house effectively lives with 2 people they consider their parents, except him. They're all much younger than him and much closer to each other developmentally. He acquired 3 much younger siblings and a step father In a short space of time. It's highly likely he felt pushed out by the new family.

You've done nothing wrong in letting your DSD call you mum, but that doesn't mean he can't feel hurt by it. You need to address the underlying feelings, without telling him he's wrong or immature. He's entitled to have found being in a blended family hard, he's entitled to feel hurt by this. His emotions don't have to be correct, they're emotions.

She's a 9yo child without a bio Mum in her life and he's a 19 year old young man who has never been without a Mum.

His relationship with you cannot be influenced by her and you need to explain that to him. There's a saying 'children bring their own love with them' and that is just as true for step kids as new babies.
It's not unreasonable for him to have a twinge of jealousy but unless he's ND and struggles with empathy he needs to get over it.

@ImustLearn2Cook

I was an absolute tit, at 19.

I’d like to think I could give my child some grace when their time comes

And explaining that as part of a concerted effort to help him work through his feelings is appropriate. But simply telling him to “deal with it” is not.

He is using threats to control his mother’s behaviour and that is coercive control. It does need to be addressed for his sake as much as anybody else’s.

And failing to address his inappropriate behaviour because of his feelings is not doing him any favours. Excusing his behaviour because of his feelings will not benefit him at all.

If he is not challenged on this behaviour now, he will repeat it. Every time he repeats this behaviour and gets away with it he will feel more justified and entitled to behave that way. Then the behaviour escalates. That is called environmental conditioning. And we are all shaped to some extent by environmental conditioning. It’s part of our human development and no one is above that.

In many studies of intimate partner violence, coercive control was the precursor to physical acts of violence and murder.

And while I am not predicting his future by this one incident. I am saying that it is important for him to learn right now that it is not ok to control other people by threatening them.

Exactly. His behaviour is not exemplary. It’s not indicative of someone who is mature for their age or secure. It is a cry for help. Not helping is going to … not help.

@Castellanos 00:33 post, also very sensitive and nails it
Two thoughtful post that I hope are read and considered