To let my step daughter call me "mum" ?

I would consider getting your son some therapy to try and unravel what issues he has got going on. That is very strange reaction.

We are very different, clearly. I would be showing compassion and understanding to all my children. Who are you to say he's "utterly ridiculous"?
You are not privy to his emotions!

You're doing the right thing. This is your ds's problem. It's a privilege your 9 yo sdd feels that way. If one of my adult ds s said the same about my grandson (who I care for) I'd be more than a little annoyed....
Your obviously doing the right thing ... I'm assuming that the younger ones don't have a problem.

And if ds says well I'm going to call xxxx mum I'd say are you dear that's nice.👀🙄

In the most important way you are her Mum and she hears others saying it so can totally understand her wanting her to. Would see it as a positive she loves you so much, not her fault her birth mother is absent. Personally I would accept this but make her aware she does also have her birth Mum so you are her other Mum. Xx

Why is he threatened by this little girl and not your other children? The twins. Who presumably also call you Mum? The step sister is the 'odd one out' in that respect and she wants to fit in with her siblings. She's been part of the family for 7 years and you've been mothering her for the same amount of time. I'm not sure what else you can do to help him see that really. Especially as he won't talk to you. You've done all you can to reassure him so yes at some point he does need to realise he is the one being unreasonable.

If she wants to call you mum and you’re happy with that then there should be nothing more to it. Your son is clearly feeling worried and threatened in some way, and you definitely need to try and talk to him and work out what’s at the heart of it. He probably just needs reassurance that he’s no less precious to you than he ever was. But don’t give in to his threats either- he needs to know that’s not an adult way of handling things you’re not happy with.

I would have a conversation with him and try to make him see the situation from the 9yo's perspective. Try to point out the difference between his life and hers. He has 2 parents that he sees and who love him even though they aren't together. He has siblings who (presumably), love him and he, they (again, presumably). He, hopefully, feels like he belongs within the family all of which this 9 year old little girl wants as well. Tell him that he will always have a mum who loves and wants him and ask him why he believes that your DD should not have the same. Finally tell him that her calling you "mum" takes nothing away from your relationship with him anymore than his siblings calling you mum does.

I’m not sure if I’ve misread your message sorry, it reads that you would possibly show more empathy if it was a DD? But feel free to correct me if I’m wrong.

Sorry, that wasn’t clear. II would expect more empathy from a teenage girl. (bit sexist, I know!)

I’m not sure if I’ve misread your message sorry, it reads that you would possibly show more empathy if it was a DD? But feel free to correct me if I’m wrong.

I do agree that’s it’s hard for OP. But I don’t think it’s impossible.

As someone else has said I think a third party would be a good option at this stage

And I said guessing.

It’s hard for OP to explore how he’s feeling if he won’t even talk to her if he doesn’t get his own way.

Agree. It's hard for OP full stop. She has her hands full in every direction.

I think the fact she's on MN shows that also.

I think some sort of discussion with a third party would be appropriate here.

He hasn’t experienced any more “constant change” than thousands of other kids.

And a lot more behave a lot worse for a lot less. But who cares? It's not top trumps.

I’m not implying either way but I genuinelly wonder what the comments would be if DS19 was actually a DD19. His emotions and feelings are completely valid on the matter. He is allowed to feel however he is feeling and it is up to OP to try to explore that with him and help him to get to a better level of understanding, which I imagine will include addressing some deep rooted worries of his.

Can’t speak for others but I’d feel exactly the same if it was a DD. Possibly to show a bit more empathy. It’s hard for OP to explore how he’s feeling if he won’t even talk to her if he doesn’t get his own way.

You made made up that he can't remember anything about his parents being together

I said probably.

Other than the guess at the time of separation (which I have said is a guess), which bits are made up?
You made made up that he can't remember anything about his parents being together, we don't know, presumably he changed from primary to secondary and maybe again for a levels. And unless all four parents live together that would be a new home.
We can even put in that he had time when it was just him and his mum in the home.
He may not have experienced more "constant change" than thousands of other kids, but other kids have gone off the rails for lots less.

You’ve made quite a lot of that up. Parents separated 15 years ago, he probably can’t remember them being together. OP hasn’t mentioned new schools or homes. He hasn’t experienced any more “constant change” than thousands of other kids.

Totally unreasonable for him to begrudge a little girl this one thing, when it sounds like he has loving and supportive family members coming out of his ears.

He doesn't need to refer to OPs husband as dad, because he has a dad. Very selfish IMO.

I'm guessing that the DS has had 10 years of almost constant change.
Again
Parents separating.
New home
New schools
EOW possibly one day in the week
Dad's new partner
Mum's new partner
Two marriages
Twins
Step sister
Possibly new family on the dad's side
etc. etc. etc.

He has done well to come out of this as normal as he has.
So posters need to learn some empathy for the boy, because its easy to see why so many boys turn into shit men if we are going back to the "man up" BS.

I disagree, he isn’t making it all about him. He’s just experiencing a certain level of confusion / worry / whatever else that he is expressing in the only way he knows how. He is still very young himself. As humans at 19 our brains are still very much developing.

There is always a reason behind behaviour and I’m tired of reading comments which are not considering his feelings and needs.

I’m not implying either way but I genuinelly wonder what the comments would be if DS19 was actually a DD19. His emotions and feelings are completely valid on the matter. He is allowed to feel however he is feeling and it is up to OP to try to explore that with him and help him to get to a better level of understanding, which I imagine will include addressing some deep rooted worries of his.

I also completely agree with those saying that SD calling OP mum is lovely, and I definitely don’t think OP should stop that if it is something that feels natural and not forced.

However I think the situation here now is more about how to approach the situation with DS. And about understanding his underlying concerns and needs. I’m not saying every 19 year old can be excused for behaviour because their brains are still developing, however a little more compassion certainly wouldn’t go amiss.

I don’t doubt that OP has compassion for her DS in this, it’s more some of the comments on MN that I’m referring to. I certainly would not want a DS of mine reading some of the comments on here aimed towards them, if this was my thread. Absolutely no compassion at all for him from some people.

Whoever thinks he needs to “get over it” “man up” “be shown the door” and whatever other awful comments I have read really should take a look at themselves rather than commenting like this about what could be quite a vulnerable 19 year old.

Honestly some people should be ashamed of themselves.

But nothing will change materially for this young man. He still has his mum as he has had for all 19 years of his life. He has a job, friends, a girlfriend, a social life, so probably not even home all that much. OP hasn’t discarded him like a snakeskin; it’s not her who is giving the silent treatment! And she’s certainly not discarding him by letting a little girl who has been abandoned by her own mother, call her ‘mum’.

WE know nothing will change for him.

This isn't logical. It's irrational emotion.

100% SD should call you Mum. Bless her heart, it must have taken an awful lot of courage to ask and risk rejection again.

Your son is a separate issue. Telling people to grow up/get a grip... I thought we were better than that by now. He feels what he feels and although he doesn't get to tell you his step sister can't call you Mum, I think it would be unwise not to listen. In an ideal world we would all be able to process and deal with every human emotion at 18, but a look around us tells us that is far from the case.

As an outsider it seems like he feels insecure about his place as your child, maybe that is actually made worse by being 19 and being on the verge of leaving home. Please reassure him over and over, ignore the threats that is just the small boy inside of him, spend 1 on 1 with him if you can and love him through it.

But nothing will change materially for this young man. He still has his mum as he has had for all 19 years of his life. He has a job, friends, a girlfriend, a social life, so probably not even home all that much. OP hasn’t discarded him like a snakeskin; it’s not her who is giving the silent treatment! And she’s certainly not discarding him by letting a little girl who has been abandoned by her own mother, call her ‘mum’.

OP is the matriarch of the family; for this little girl to feel part of the family (and this is her only family) she should call OP mum. I am really quite surprised she hasn’t until now. This young man is making it all about him.

It's wonderful that DSD wants to call OP mum.

But to tell a 19 year old he's a bellend, show him the door, tell him to grow the fuck up?

A 19 year old can be just as immature, afraid, irrational as the rest of us. He's an adult but a very new one. He clearly is very affected.

I think OP will handle this with as much compassion as is needed. Her DD needs her and so does her son.

Absolutely he is hurt and insecure about his place in the family. And yes: he’s 19 not 9. But isn’t it good that his place in the family still matters to him? I’d be more concerned if he’d eaten your food, slept in your beds, then discarded you all like a snakeskin.

So many ugly responses aimed at the son for going against the holy grail of MN when it comes to blended families and not playing ball, as in shut up and put up.
Mum has bought a new man into his life, a new step sister and then two twins. I think deep down he is hurt and insecure that he has lost his place in the family.
He is not being internationally unkind but honest. It's not his SS he is angry with but his Mum.
There is a very unrealistic belief on here that kids should just suck it all up and get on with it, that maybe the case when kids are young but not the way it works with older more assertive kids in real life.