Yes, a stepparent is free to do that, and then later we hear the stories about shitty step-parents and how shitty parents allowed a shitty situation to happen while the children grew up
Cause really, nobody enters a relationship with someone who has a young child and expect to basically be hands free, maybe you shouldn't go for parents then :v
As for the house, ok I guess I completely missed that, it does change some of the context cause then everyone else is an outsider
It also changes one big thing, if it was his house then she was the outsider and him and the children have technically priorities over the house, she's uncomfortable enough? She could leave yet endured the situation for years, so it's on her
I didn't hide at any moment I think this entire relationship is sus and OP is maybe hiding some details about how things are
But like, I admit maybe this is kinda of a double standard, but if it was the husband house, 100% the child home, there's some room for them do be petulant cause hey, it's their house, but that's not the case, I feel if you marry someone and bring your children to their house you have even more obligation of making them act better
Anyway, it changes things because of one single detail, if it was the husband house then the children would always be expected to be there in some way for years to come, so OP choice is literally endure it or leave
But with it being her house she doesn't have obligation of welcoming any of the children after they turn 18, from the way the father is I don't think he would care much either
And before anyone try to play gotcha, I don't mean legal obligation, you know what I'm talking about so don't be obtuse :v
So OP options change from waiting it out and leaving to wait untill the son is 18 and not allowing him back or kick everyone out
Again, I do think something is sus and there's a lot not being said about how the children really are treated
But as much as I feel something wrong your house is your house, the mistake was letting it go for so long when she has all the leverage, so either force things to change or cut it out
Even if you're a shitty person and is doing something wrong you're still the king / queen in your own castle, so the uncomfortable people who gets to leave if you decide go be petty enough