Wait, so you visit the family home? where does the ex go?
Mate, I reckon you just get a house set up and tell the kids to vote with their feet... Frankly, they can tell mum that if she is gonna be a twit, they'll stay with you... I never advocate coaching kids, but lets deal with some realities here. Mate, I told my kids that I love them, love their mum and i hope she is happy (with a hint of sarcasm). But they heard me comforting them, telling them all would be ok etc.... That 'brain washing' worked heaps better than the nasty crap my ex said to the kids about me... Infact her antics became my best asset in trying to fix this crap. The more the ex went stupid, the more sane I looked and the kids need at least one sane parent.