Good luck! My EX too tried to do that....and at the end, I won them over and they wondered WTH because they didn't like the new "wife" he basically traded me in for. I kept saying OH well, there's nothing I can do or want to do, I'm moving on and I'm ok. I too traded for a new husband, and the difference was that folks liked him....(but over time he changed....and so he got fired by me as well).
Maybe that's something that needs to be worked on. If the kids go to a public event, both parents should be there and feel comfortable being there. My MD's husband has an EX....and its really wonderful how they all get along and I even get along with her. Now that doesn't mean I don't like some of her quirks which is why there was a divorce, but the daughter is put first.....
I wish EX#2 of mine would figure that out. EX#1 has....and we tolerate each other's presence and can have short conversations and important conversations, but it took him YEARS not to be an outright butthole to me in their presence. The kids got it more than you know as to where the fault was,
And that was my point in sharing this....the kids do get it many times.