Need advice on how to change things around please.......

[Harrypotter10]

My 11 year old ss (I actually never call him my ss just my oldest son which I will now refer to him as) can’t stand the fact that my 8yr old daughter and his other ‘half siblings’ have their mum around and is especially horrible towards my daughter because of it. He has a hot head like his father and can be quite undercover malicious towards her but never in front of his father. He’s the total opposite when he’s elsewhere-caring, thoughtful and he’s actually a very sensitive young child, but he's worn me down at home. To the point where I just want to pack me and the other kids up and leave. I stupidly left parenting up to his father and nanny ( mil lives with us and looks after the kids while we’re at work and yes I get along with her very well) which has backfired massively.e.g if I have to tell him 2-3 times it’s time to have breakfast he immediately gets defensive, starts saying I treat him unfairly compared to my daughter (I most certainly don’t) and then starts taking it out on her with the under breath comments, lashing out because she turned her head towards him etc. Stupid shit. and no I’m not an angry, raise my voice, smack my kids kind of parent. I’m quite happy to explain why I’ve said or done something but also firm in the fact that I am a parent 1st and friend 2nd. He’s like his mother and only sees and hears what he wants to which drives me up the wall. My question is this, how the F@&K do I turn this around because I feel like I’m just standing there while he a) bullies my daughter, because that’s what it is and b) because I resent him even though I know his life has not been an easy one (fried mother who has never really been ’present‘, his fathers parenting left a lot to be desired before I came along and still does in my honest opinion). And please don’t start with the “your a bad person bulls@&$”. This is how I feel and now i need advice from ppl that have been here, on how to turn it around. Feel free to ask any questions too. There’s obviously more to the big picture than I’ve just written.

Thanks very much in advance 🙂

You sound very caring. I dont know if it's any help my my 12 year old is like that with his 9 year old brother. And kn the last year I feel I have to ask him 10 times to do something then hell raise his hands and voice very indignantly saying what? What did I do? You always love d3 more. Then will treat ds2 like you said.
I'm thinking it's a preteen thing, not necessarily to do with step parenting but its exhausting to keep my cool.
What I do is completely ignore the protestations, move him away from his brother and when calm have a chat about it. But I feel although hes super clever, he feels in the right when he behaves like this

What does the bullying of your daughter look like?

If it is severe and no changes with correcting his behaviour I would honestly be getting my daughter out of the situation. It’s not her fault he doesn’t have a mum around and that his dad doesn’t parent him well.

Your daughter’s mental and physical safety has to be your priority. That doesn’t make you a bad person.