To let my step daughter call me "mum" ?

Your son sounds like an absolute brat as well. I wouldn't pay any attention to him and his horrible issue with your daughter.

Your 19 years old is jealous of your 9 years SDaughter. He needs to grow up.

Your son is being a bell end but something is going on. His reaction is too over the top so something is worrying him.
Has he said why he feels that way to your husband or to his dad? However you said you wouldn't be happy if he called his step mum mum so can you see how he feels?
I think he probably feels replaced. He's an adult, talking about moving out after university and now there's another child calling you mum. He probably feels that you don't want /need him as much.
I would try and spend time with him, don't say you love him, show him.
Having said that he has absolutely no right to say what your daughter calls you. I think it's beautiful that she sees you as mum and wants to call you that (but I'm not 19).
Keep that closeness with her but try not to let your son feel pushed out.
I feel for because you sound really caring but are juggling so much.

Your son does need to grow up. He’s a teen and they are notoriously selfish so perhaps he genuinely can’t see this little girl is the only person in the household without a bio mother who loves her and puts her first. What she calls you doesn’t change the relationship. He’s jealous of course and you probably need to keep getting to keep talking to you. He needs to see how selfish his actions are, and more importantly he needs to know he cannot dictate or threaten you. He’s an adult now, he can move out if he’s genuinely unhappy with the situation. I’d feel a bit upset I’d raised someone without compassion but I’d also think my eldest might be a bit similar so this is no reflection on your parenting. I was very young when he was born and it was just him and I for a long time.

It’s a beautiful thing. You’ve done a lovely job. I call my step dad, Dad and there’s nothing wrong with that!

You hit the nail on the head there though even though you didn’t mean to - you said “we all understand our fostering”.

this wasn’t a joint family decision. This was a single parented kid suddenly finding himself with a much younger step sibling and step dad and then getting more siblings. He’s the only one with a different dad. He didn’t make some lovely family decision to have her. He was just a kid whose mum suddenly got a new family he was on the outside of.

not saying it’s right - but clearly it’s how he feels.

Yes @Devonshiregal is right.

He was an only child for a long time and had all your attention, then has to put up with a new partner and his daughter moving in, then the twins come along. Your attention has shifted to the younger ones.

He might be 19 but he's still at home and needs your love and attention even if he is being difficult. There has been a little of change in his life.

I agree with this. He's an adult and is being very cruel about a young child who clearly craves a mother. Is jealousy but he needs to overcome it and stop being selfish.

😂

I agree with Yoda here.

Of course, you aren't being unreasonable; your Son is! I called my stepfather Dad because, well, he was a Dad to me. It sounds like you are being a Mum to your SD and she recognizes that. Give him time, and continue loving him and he'll most likely recognize that as well.

Yes, you’ve nailed it.

Actually, I withdraw the phrase 'teenaged petulance'. @Devonshiregal has it spot on.

If the child wants to call you mum let her. She clearly needs a mum and wants to feel that level of closeness with you.

your son is a dick. He is acting like a spoilt child. This little girl has been his little sister for five years. How can he be so cruel? I would be concerned for his character and emotional maturity.

it doesn’t bode well for the man he is becoming.

She is her mum.

@Lospecesenelrio lots of posters are saying your son needs to grow up. Well, yes, but maybe therein lies the heart of his issue? He's 19 - only just into adulthood and about to fly the nest, leaving behind siblings and a step sibling who are far, far younger. It's a big transition and he's probably feeling anxious and insecure.
He may be 19, but he still needs your guidance. I'd stand your ground and say your stepdaughter will be calling you mum, but be aware that you might need to meet a bit of teenaged petulance with patience and understanding as well as firmness.

Thanks OP, I was wondering about the twins too. At least it's not because she's a girl, then.

His "aren't three enough for you" comment was quite something.

For fucks sake stop calling him immature and childish op. That is not going to help this situation.

Your step daughter REPRESENTS an issue he has with you. This may have started years ago when you met William and he felt replaced. It might have started before that. It might have started after - perhaps he had a single mum working, distracted, then William and this girl came along and you seemed to pay more attention to her in his eyes but the reality for you was you had more time to relax due to joint income from William…I don’t know but this jealousy started somewhere.

Honestly it could be anything that caused the jealously but he is your son and it’s your responsibility to look honestly at yourself, your history with him and figure out why he’s so insecure in your relationship.

He was what? About 12, when he had to make room for her as a toddler? No doubt watching you pick her up and play with her and have a new family right as he was entering teenage years was tough.

Does he like her well enough? How do the get along? This hasn’t just come out of the blue - even if he’s kept it well hidden, he’s been envious a long time.

Of course you should let your step daughter do what she wants re calling you mum. It’s important for you and her and it’s great you have a lovely relationship.

But listen to what he’s been saying - he’s telling you repeatedly he feels shunted out by her. He’s telling you he feels like you like her more than him. He’s telling you he feels second best. The one thing he has over your new family is that you are actually his mum, and now you’re giving that away too.

he may be 19 but he has feelings and they’re valid. The reality is we all want our parents to love us and approve of us no matter how old we get. There are adults on here every day talking about how this sibling is the golden child, or that sibling got more attention, or their parents never spent any time with them, etc etc and they’re aged 20-100. Parental rejection, whether real or perceived hurts at any age.

And 19 is still young. He’s still got a good few years of fucked up decision making before he becomes a fully fledged adult. When he’s 30 he’ll be ready to repress his jealously and direct his complaints to his therapist for the sake of keeping the peace. Right now he’s a teenager who feels he’s not special to his mum.

No child gets a say in who else their parent is a parent to. Tell your son he is no different to any other child (and I’m being generous in referring to him as a child)

Are the ins boys? Is she the only girl?
This is sounding a very unpleasant environment for her to grow up in. Having already been abandoned by her mother, to then endure emotional (at least!) abuse by her stepbrother. You need to get a grip of this situation quickly or she is going to be severely affected.

I can’t believe some PPs are suggesting you tell your DSD not to call you mum! How awful! Imagine a little girl who has been utterly let down by her biological mum, builds up enough of a relationship with her step mum to want to call her “mum” and even wants to be adopted all for the step mum to say “no”. It would be heartbreaking.

Your DSD is lucky to have you OP!

Have you shared any of the details (like the letter) with your DS? Maybe this would make him see things from DSD’s perspective.

From your updates, OP, he does sound like an unpleasant young man, and while he may not overtly bully your daughter, his attitude is all too clear. He's going to have to like or lump it, not to mention doing a crash course in growing up. He doesn't get to exclude her from calling the only mother she really knows "Mum".

You may not be her biological mother, but clearly this young girl regards you as her mum. She has chosen you as her mum. I could maybe understand your son's clear jealousy if he was a small child, but he is a grown man and needs to deal with it.