If you do it, DON'T do it anonymously. Your wife will be livid if you expose them, and you want to be able to take the high road and say "I thought she should know the truth," and "I'm doing this to fight for our marriage," etc. If you do it anonymously, it will just come across as a chickenchit move.
I do think she has a right to know, however -- why should she be the only one (of the four of you) who DOESN'T???
