For what it's worth. I lived through a sitch like this with my S and her ex. He undermined and talked crap about us to the point of...well i don't have the space to fully get into it here. He had my SD15 so convinced we were horrible for a long time.
When she was 13 we finally had enough and were honest with her and she had matured enough not to be manipulated and understand what destructive behavior looked like. She finally confronted her Dad and things have straightened out now.
What i'm getting at is that kids are smart. They get alot more than they we think they do sometimes. He is destroying HIS relationship with them. Stay steady. They will remember that in the long run even when it seems hard now.
Your not always going to be in this place.
Hang in there. they will thank you and respect you for it later!
V
***Getting up every day and learning to breathe in a new me. For me and my children***
Me: 43 W: 38 SD-15 S(s): 12,9,7 Separated-2/14/2009 My sitch