Hands down best thing my step daughters did for me was housework. I didn't know how to ask or what to ask for, and one day after visiting their dad they just stepped up and did laundry dishes, etc. When I came out of our bedroom to a clean house, my heart just filled to bursting with love and some of the massive weight was lifted.
Sometimes, for me, just trying to make another decision (what can you do to help?) was impossible. Especially near the end.
Having someone just DO IT was amazing.

If his mother is there to be with him, try to get her out of the house for a while, even if it is just a walk around the block.
Let her cry, let her talk, hold her hand. She is blessed to have you, Becky.