1. Your wife will be FURIOUS, and will spew all kinds of things at you like "Now you've just blown ANY chance of working this out with us!" This is typical script; they all say it. It soon blows over, but there WILL be blowback.
2. I can't think of any more "con's."
Pro's:
1. It will hasten the demise of the affair. Affairs thrive in secrecy, and in the romantic, taboo "mystique" of it all. Shining the light of day on them shows their warts more quickly, and usually (not always) kills them much quicker.
2. It shows your wife you're willing to fight for her. Women tie their feelings of "respect" very closely to their feelings of "love," and when a man sits by passively and doesn't fight for them, they often lose respect for them and -- therefore -- love starts to slip as well.
3. The OM's wife has a right to know, and to make her own family decisions accordingly. How fair is it that she be the ONLY one of the four affected -- seriously, life-alteringly affected -- that DOESN'T know the truth?
There are other valid pro's and con's, but I think those are the most important ones. There are those who will say "it will only drive them together," but I think that's a bunch of hooey, since -- guess what?? -- they're ALREADY together, and cheating on their spouses!
One important cautionary note, however: you should ONLY use exposure as a tactic, and part of an overall strategy to SAVE your marriage. If you're "done", and only doing it out of SPITE, then you shouldn't do it.