Thanks for the input. Without getting into a lot of detail, I have rethought my relationship with the in laws. I need to back away from them for a while. I do intend to share with them what I know of my wife's plans, though.
Regarding the R talk. It's time for the last resort. I will lay it out and tell her how I feel, and I have no doubt it will get me nowhere. She is deeply, passionately in love with a person that will break her heart and leave her twisting in the wind. Of course, I will not say this... what I will say is that, for the sake of the kids, let's get to work on us.
It will be a wasted effort, though. She wants none of me and all of him.