LW1 has a husband problem not a MIL problem, but IMO so does LW4. What do you bet he wants to keep all his family traditions for every event?

I give that MIL the benefit of the doubt only in that

But, oh, I should add that his mother doesn’t believe in unmarried couples spending holidays with his side

may only mean "my living room is only so large and there's 37 of us already and once cousin Sue tried to bring all three of the guys she was dating and we ran out of nachos."