Dixie, it's just sad what addiction does to families.
I can't see either of my son's children (2 different mothers, 2 different cities) because they are protecting their children from my son. He has never ever been abusive and loves both his children, but he has never been consistent in his recovery or visits and commitments to them and that has had an emotional impact on these children and the mothers are protecting against that.
While this hurts very much, I respect both these women for protecting their children. Whether I agree or not is not relevant, what's important is that they are doing the best they can and even if it isn't perfect, I bow to their efforts.
I know several moms here who have lost their grandchildren because of their sons' addictions. It's sad, tragic even, but it is what it is and there is nothing we can do about it.
Your son must decide if he wants to pursue this legally, he can and may have a good case. But in the end it's what is best for the child that should come first.
I'm sending hugs because it stinks to be us sometimes, in a perfect world we'd both make wonderful grandma's. I hope your story has a happier ending than mine, really I do, but felt a need to just say what I said.
Hugs