SS,
Thanks for this suggestion about a boundary.

I have been worrying about him saying these things to the kids rather than to me.

He only phones them now, since I started not being so responsive to his calls.

In relation to the parental alienation approach - he will say that i am doing the same thing. This has been his line for a while. He senses the kids slipping away from him and blames me.
He now argues to them that i am poisoning their minds about OW as well.

If it goes to court, it will immediately devolve into a: "You are doing this", "No, YOU are", argument.