Sorry about all of this. You might be able to specify this in a mediation agreement - but your W would have to be on board.
I know this is a bitter, bitter pill to swallow, but unless there is some sort of active criminal behavior going on, most states don't care about this. You won't be able to keep him away from them if your wife is determined to have him in their lives (there might be exceptions- you can always consult with an atty)
Maybe some others have managed to set some effective boundaries around this, and if they have, I hope they chime in.
I wish I had better feedback for you. My STBX moved directly in with the OW and immediately exposed the kids to her. There's nothing I can do about it.
