@80sraised,
That was a hard decision to make, but I think the right one. They had their chance to come clean but chose not to.
Your friend deserved not to marry a woman whom's body belonged to someone else, I can't imagine that affair would have stopped, had he not have found out, to then be found out once he was married, that would have been 10 times worse.
You're a good friend.. Your brother will get over it, you have your parents support in this as well.