Dear Miss Understood, I've just gone through the same thing and I'm a few more months along in the process than you.
I can't speak about your son, but I don't think it matters which one of the spoiled brats is in the lead, they are both united, as is my future DIL and son. My son is playing the Passive "who me?" game which allows him to play the innocent and the bullying and aggressive DIL is seen as the victimizer. Every victimizer needs a victim and she already has one so I'm not prepared to give her another. He chose her for himself, and I am opting out of this "package deal".
I've been through this type of scenario in the last few months and have been through the despair. I'm on the other side now, and determined to live my life on my terms and only allow anyone else into it if they meet my terms of courtesy and basic consideration. Obviously the Groom and Bride to be don't even come close to getting on the radar in terms of manners, but that is their problem. I've come to enjoy the "silent treatment" and not see it as a form of punishment but more as a type of "peace and quiet", solitude from their drama and games, etc.
I think the 2 months that you have lost is part of the process of dealing with this situation and I have decided to get on with my life and leave "frick and frack" to their games, etc. There are people who get pulled into those games, but I don't think they are worth worrying about. If they don't have enough backbone to stand on their own two feet instead of being pushed around by a couple of kids who should have better things to do.....well, forgetabouthem.
I'm with you, give it up, so you can let them inflict their misery/hostility on someone else and get on with your life and have some fun while you are at it.
You only live once so ya gotta make the most of it.