You tell DH you aren't participating and if he does then you will decide what you will do. I told my DH I wont under any circumstances go to ball games, since his ex will be there, I refuse. I told him he could go if he wanted, but hanging out with his ex all day would not have a good result for him in his marriage to ME.

He's decided to refrain from going. I dont want DH to neccessarily miss out on things with his kids but his EXW will sit with him and try to be a happy family and I told DH that just confuses these kids even more.

I think joint birthday parties are unnecessary.

As for the religious celebrations those can be tricky as there is usually a mass followed by the party and I think it would be inconsiderate to invite people to the mass but not have the party until a week later or whatever. I mean I would be annoyed if I had to carve out two days to celebrate something because two adults who used to be married can't be in the same room for two hours.

With that said, we had a joint party for a religious event and the party itself was fine. Our families hung out and BM and her husband's family did their thing. All of the kids just meshed and played. Buuuutttt, I know for a fact we ended up on the hook for A LOT more money and things were not split down the middle evenly so I would not want to do it again.

The only time this is necessary is when the event is not under your control, i.e. high school graduation. You may have to all be there for such events but even then you don't have to sit together.

Separate parties for anything else are a must. The children need to accept the fact that their parents are not together and joint parties give them the false illusion that the family unit still exists.

If both parents are OK with having joint parties(are able to get along, both want to save money, neither one has hopes of getting back together...), so be it. That doesn't mean SM has to agree or attend.