Brief update. YS is no longer overtly manic, though he still seems unstable.
He is in a rage about everything and everyone connected to my wife. Apparently I was the target of his ravings at the most recent therapy session.
The estrangement will be ongoing and I suspect lengthy. He is not open to hearing one positive word about anyone on wife's side of the equation: wife, grandparents, me, anyone. We are all evil and his dad is perfect. His thinking is very rigid and black and white.
He is attending school regularly. He is exhibiting many of the same poor habits here as before (not working productively in class, etc) but he has much more support so he is getting through with grades ranging from Bs to Ds.
Wife and I are doing fine. We are busy with other aspects of life. For myself as stepparent, quite honestly, I feel the drama YS brings to my life is not worth the reward of whatever limited contact he may be willing to endure. I am stepping back and out of his life totally. I will support my wife and of course will always be as civil, kind and patient toward YS as I can be. But I am done with my emotional investment in him.
This may sound harsh but it's what I need to do for my sanity.