I agree with Dudess but I'll add another point, if you're contacting your wife's parents to get them to side with you on this, don't bother, it never works out that way, they will always side with her before they side with you. That's their kid and you're just the son-in-law, you will usually always lose in that situation.
Contact the OM's wife and her sister first and leave it at that and wait for the reply back. Even if the OM's wife is planning to leave him, this will still add ammunition to whatever plan she has in store for him.
