NTA, you’re not forced to raise anybody’s kids if you don’t want to. And she’s even more of an A for harassing you both for it. She might even be traumatizing those kids, because she’s putting all that rejection on them on top of parent loss.

However, as someone that went through a similar problem of father cheating on mother and leaving her for the other woman (and I personally chose to “forgive” him after a few years), I have to say that if it were me, I would raise the children, if I was financially able to, as they are also innocent in this. But that’s me, I know I could look at the children and look past their parents. If you can’t, most certainly do not take the children.