Ok, I see the reasoning behind telling her what you know in front of the family. Sounds like you need witnesses unfortunately. I'm sure you have done this already, but have you closed joint accounts at this point? You wouldn't want her cleaning it out secretly. I wouldn't normally say to expose her in this way. But, it looks like it is necessary.
When you have this confrontation with the family....make sure that you say that you are fighting for your marriage.
Best case scenario- You tell her what you know, she confesses, apologizes, agrees to "no contact"/full transparency, and you both see a marriage counselor and start the repair work.
I'm guessing it won't go that way. Maybe more along these lines- You tell her what you know, she denies, you end up having to show proof, you tell her that you love her and are trying to repair the marriage and give it a chance but that is impossible with a third party, she gets angry, throws any and all of your faults out there (and some lies), her family put some pressure on her, she breaks down and agrees to "no contact"/full transparency.
Worst case scenario- She denies it all, her family disowns her, she hates you, and a bitter battle ensues.
