Hi Respekt--
He could just say "Respekt and the kids aren't coming today. We've discussed it and I'm OK with it, and I don't really want to talk about it. Next subject." If they press him he can firmly state "Leave it. It's a private matter between me and my wife." He's telling the truth and opting out of any drama.
Could he ask his sponsor for some tips?
Respekt you're doing the right thing for you and your kids so try to detach from the outcome. What his relatives, who you say are still active alcoholics, think of you and your decisions really does not matter. And your H, who is still learning how to live life as a sober person, has to pick his way through these emotional minefields on his own.
Peace,
B.