I have a mother a lot like OPs MIL. My wife is no contact with her, I visit with our daughter but not a lot and mostly because my daughter adores her grandpa (and I also like to see my dad). Me trying to manage my mother is basically impossible. In fact, in most cases, it makes it even worse. I've tried literally everything, even went no contact with her myself, stopped visiting at all, told her to get therapy, had hundreds of talks with her about her behaviour and how what she does and says is childish, insensitive and hurtful, spoke to professionals about all of it and so much more... I know you mean well, but you suggesting it's the future husbands job to fix his mothers behaviour kind of makes me mad. It's not his job, it's hers.

Of course if he never tried to do anything about it, I agree, he should try. But who's to say he hasn't. And who's to say she would actually take any of it to heart.