I get it...the question is how can I force either one to not show up without telling the whole family what is going on?
Why are you helping them keep it a secret? I think you need to get to the point where you are just sick and tired of being a doormat, and you just say "enough is enough" and you tell your W that you are done with her and her BS behavior and she is no longer welcome in your life in any way shape or form including going to family events. Then you explain to your family that you and your W are done and you would appreciate it if they no longer invite her to family events since she is no longer a member of the family. It doesn't sound like you are there yet, but just ask yourself if you don't deserve better than this misery.
Your sitch just reminds me so much of TXHubby's and I really agree with Sandi that your W is going to be content to cake-eat while actively engaging in an affair and she will continue it indefinitely, unless she gets the wake-up call that it is all going to come crashing down.
