This is bworl (Bill), not Deb13. We just got back from our honeymoon, she was logged on and I wanted to check in on you. Catching up and seeing some of what was on the horizon and I wanted to chime in.
I'm going to come down pretty firmly on the negative side regarding vacationing with this couple.
Your wife is PERFECTLY clear on how you AND your boys feel about this couple. The fact that she gets some strange satisfaction by being with them is not sufficient to compel you to invest a weekend with them.
I know this sounds absolutely out of left field and crazy, but have you considered that the weekend away with them could be some sick introduction to swinging or the like?
The bigger point for me is that these people have many times over shown themselves to NOT be friends of the marriage. Truth is, they don't even sound like very nice people.
I think this is one that you should hold firm on. Call it a mini "line in the sand moment." You don't have to go all George Patton on her, but I think it wouldn't take much to point out that both you and the boys have had significant issues with these people, and that you would LOVE a weekend with her, but NOT with their company (which would make it very much NOT a weekend with her).
This is a viscious ride, as you are learning. You have some extremely good counsel on your side. Continue to remind yourself that you are NOT the problem here. YOu can lovingly support your wife and her search for answers, but you are not called to sacrifice your integrity or standards in the process.