Ugh - sorry you are going through this - just know this is not unique, it is a mirror image of conversations I am having with my RXAH who is in early recovery.
You have nothing to feel guilty about - as for me, I have to gently remind XAH to stay on his side of the street and try my best not to engage. After I ignore him long enough he starts sounding a bit more coherent.
As for his mom - I am sure she enjoys time with the twins - if she starts trying to guilt trip you - sit down and explain what goes on and your rationale. This is true that you don't own her any explanation - but for me it made my communication with ex MIL so much better. She is still hurt but she has divorced an alcoholic herself so she can relate.
Hang in there - it will be better