Yes it happens more then you ever hear about. Many times girls are too scared to come forward because of threats & mothers who don't believe them. Or mothers who look the other way. Where have you been, stories like this are in the paper all the time!
I would just make sure all the DNA matched, convict them, make sure they got all involved & kill them asap. I have no mercy for scum like this. Nor do I like paying for scum to sit in jail & cost us money for appeals . If they are 100% guilty then rid the earth of scum like this IMHO.
Often, the wife either knows or does not want to know, because she doesn't want to lose the man over it (for either financial or emotional reasons)