If I was their mum the girl would not be welcome to set foot inside my house.
That’s all very noble, but what if there are e.g. children involved? Do people think it’s ok to deliberately ban say, their grandchildren’s mother from their house?
I think that while people will have their opinions, family should, as a whole, stay out of it. What happens between the brothers is between them, but people moralising over someone else’s actions is partly what causes the family divisions.
FWIW I knew someone whose dad left his mum for her sister. For a few years they didn’t speak, but then they made up, and remained very close. The sister would regularly go round to her sister’s to visit, with her partner (the sister’s ex) as well, and while some might think that’s unconventional, it’s one of the more healthy setups I’ve seen in a long time. All this moralising and retribution and deciding who should and shouldn’t be spoken to is what causes family divisions, and bad atmospheres.
It’s far too simplistic to say that the people involved are the ones responsible for what happens, but truth is that the people around them are responsible for the way they react.
If I had two sons and one did this to the other, while I would make it clear I didn’t approve of what the one had done, I would leave it at that. My children would still be my children. The wrong wouldn’t be mine to forgive, and while I might not like what they’d done, that wouldn’t stop me from loving them or having a relationship with them.