NC, Your sitch is just as FUBAR as mine! I stopped posting as well just because what I am going through is so extreme.
The OM in your sitch and the OW in mine are a "fine" pair (as are many OW/OM we read about in DB). I would not want to trust my children to such a schmuck either. So much for my words of wisdom!
Karen has a good point about your ex doing things just to antagonize you. You certainly can't ban them from attending the events, and you'd catch h3ll if you don't tell them. At least you have a parenting coordinator to help mediate things. If that ever happens to me, and I'm forced to attend an event with OW in my sitch, I would vote to take the high road and maintain class, character and integrity.
Funny thing about your ex demanding discretion! My H is the same way. Doesn't want me talking to anyone about what he's done or is doing, but it's ok that he continues to lie and sneak around on me. I think the proper word here is hypocrite.
Karen, I'll try to post an update sometime this weekend.