LW - REALLY sorry i have been so out of touch - i didn't manage to reply to Friday's e because of work and have been on family missions all w/e.
A couple of things - yes, he's being human atm - but that's human for him. All those threads you see in chat 'I'm fuming with DH...' 'DH is an a*' etc etc, are women outraged because their DH has done something humiliating, rude and nasty like tell their own mothers that they are boring. Repeatedly. And THEN, instead of apologising, have blithely sworn at them at the end of the night.
And something else: IF my DP insulted me to my Mum, or dad or any toehr blood relative, my Mum would tactfully but firmly let him know that insulting her daughter and expecting her to agree wasn't accepatable. When you are a MIL will you be planning to collude with your DIL in slagging your DS off at family gatherings? i doubt it! Sorry - but your Mum is totally out of order - and to refuse to help you with a mouse because it upsets H is ...well, i am speechless.
I think do think you are right NOT to tell your sister what is going on atm - given the tinderbox situation, and also in case anything erupts over Xmas - too much advocaat down any one person's neck and all hell could be let loose! If you can, just put it all at the back of your mind, in a secret cupboard to which only you have the key, ride it out...and tell when plans are clear and you know exactly what your sister can do to help. But it's very good that your sister recognises how nasty your H was at the 'do' and how bad your Mum's response. She's a v good ally, I think...but you can bide your time.
And honestly, talking about and to you like that is NOT good enough.