No, the dad is the one to blame.

you can't pretend it would make any more sense for them to blame it all on their dad and be BFFs with her

But it would make more sense? He's the one who made the choice to cheat. He's the one who caused their parents to divorce. He's the one who broke up their home. Hating him is normal and natural.

Hating her for being in love with a scummy guy is just... bullshit. Especially when we have no idea whether she even knew he was married when they started dating, what he told her about his marriage, etc.

For the rest: Like I said to someone else, I'm not saying laop is sexist for hating their step-mom. I'm not talking about laop's attitudes at all, I understand that they want to keep their rosy-glasses view of their father and keep loving him the way they did and so they couldn't put the blame for his actions on him and had to displace it - it's not fair, it's kind of gross, but it's not based in sexism or anything like that.

When I'm talking about sexism I was talking about the comments here and on aita and stuff that are putting all the blame on the dad's wife for his cheating and saying that she's the one "at fault" for his cheating, for the divorce, etc. Pushing the blame for a man's actions onto a woman is sexist.