About the visitation schedule, with kids as old as yours, they would probably get to choose. How can you "make" a teen do anything, or anyone else for that matter?
If you would truly like him to spend more time with them and they are willing, you might talk with him and see what he thinks. But don't try to force something that's going to fail just because you feel he's not present enough in their live. Building Rs, or rebuilding Rs is tricky business and you aren't really a party to their R. If they want to build a R, they have to do it, in their own way, in their own time.
What are your Ds doing to help you? Letting go of control sometimes means delegating. It also means letting go of things that you do for others that they could do for themselves or things that you do because you think you should.
Got any of those? That's where resentment is allowed to grow. "Look at everything I've done for you and this is how you repay me!"
Me 57/H 58 M36 S 2.5yrs R 12/13
Let me give up the need to know why things happen as they do. I will never know and constant wondering is constant suffering. Caroline Myss