You probably feel like you are being disloyal to your son, because of the ranting he is doing about feeling you are taking side, their words still bite even though we try and let it go in one ear and our the other. Sounds like he is still playing some of that manipulation game with you. I don't know if it is such a great idea hiding the fact she is coming to spend sometime with you, somewhere down the road it might come out and that might be worse. Maybe tell him after she is gone and not to bother calling when he is in one of those foul moods.
On a better note how is Florida! This is somewhere that I have been giving some thought to for a vacation. Enjoy Moose!
Rose