FHN has the right idea, kill them with kindness. My stepdaughters father is a real piece of work, just petty and stupid. But I don't fall for it just always sugary sweet to him and it pisses him off to no end and it is whats best for my daughter. Just never badmouth your ex to your kids. I came from a broken JW home and all my mom did was bash my dad (who wasn't a sweetheart) and i started to resent her for her biterness.
I hope your situation improves