@Milkshake7489 You really don’t know what it’s like for any of the DSC involved. Or what the wider dynamics actually are.
I certainly would not try to ‘parent’ my DSC. I don’t attend parents’ evenings or things like that. Their parents do that and have no need or desire for me to have an input into that whatsoever. My role would be, for example, to look after whatever needed looking after so DH could attend. Nothing more.
Children really don’t need everyone in their life to adore them. They need people to be kind and warm and fair. I can do that. I can make sure they have a nice time and make nice meals. But I am not their parent and never will be.
DH might try to expect me to love his children, but: 1. He doesn’t love my children (and that fine); 2. His parenting choices produce behaviour that’s hard to love and he doesn’t want to do anything different (or allow me any control over how they behave in my house). So I feel no obligation other than to stay in my assigned lane and treat the DSC like I would the children of visiting friends.
My DS has a stepmother. He really likes her, but I don’t think he loves her. I doubt she loves him. She takes much the same approach as me as far as I can tell and it does DS absolutely no harm at all. He knows he’s loved by his father and is welcomed by his stepmother. In fact, he probably likes her much more than he would if she tried to the another parent to him.
It’s easy to be all emotive about these things. But it’s unfair to assume that anything other than deciding you are a fully committed extra parent who feels just like their actual parents is damaging to a child or anything to be sad about.