I wouldn't tell your wifes family. It is not your place to do so and you will gain nothing from it. It will only make matters worse and reafirm to your wife that she doesnt want you. It is for your wife to tell them if she so feels.
I am in the same position and also feel like confronting OM and letting her family know but I will gain nothing other than more heart ache and driving my wife further away from me. Over the last 2 days Ive had an awakening in that I just need to concentrate on me. Be the best i can. Be the best dad i can be
Me:40 W:35 D:8 T:13 M:10 WAW: 7/14 PA Discovered: 1/15 at least 6 months Moved out and moved on