Uh. I think you may have the causality reversed there, SEM. I don't think he's being an asshole to a kid because his kids don't talk to him; I suspect his kids don't talk to him because he's an asshole around kids.

If you feel that strongly about family, you can decide whether you need to cut him off entirely, but I kind of suggest you maybe keep it to a Christmas-cards-only sort of connection until your kids are adults and then reassess.