I believe he'll get the custody of the kids too if she goes blind, at least that sounds the most reasonable thing to happen. Parents are supposed to be ready for this, I think, no matter if they're divorced or not. Actually, his ex should rely on him for this, he's the father after all.

As for the other situations, many are out of your reach or even his. Why is his mother's diabetes out of control? Is she taking care of herself? Even if it's beyound his efforts, he'll still worry about her and this will consume his energy.

I'm sorry you're caught in the middle of this. Honestly, all you can do is keep supporting him, be patient and try not to guess in which position you are among his priorities because he is with you after all. He has too much to worry indeed and none of those sound like things he could ignore or opt out of. I understand it was such a bad timing as it's been only 6 months, but requesting more of him right now is probably the worst idea ever... :/