When I really needed a break from caregiving, my siblings-in-laws didn't give me a real break.

I have to ask for time alone. Husband doesn't like to go to store and cant leave him alone. No one but grandsons 21 and 15 want to stay. But still I hurry. Never know what will happen as his (husband with Alzhemiers) will try. So time alone is not really time alone!!

Breaks are hard to come by. I love the "experts" who say "Embark on a new hobby and go out with friends". THey say that's the way to cure burnout and depression. I'm sure they're right but it's not always frequently possible when the caregiver is caregving in a parent's home and the caregiver is unemployed and just can't just pick up the phone and call for respite care on a whim. I love my mom and we get along so it's better than a lot of these posts.
Still the other day I had to hold my tongue when my mother told me how young I still was (I'm 51) and that I should be happy that I have my life to lead. Had to hold my tongue b/c how am i really enjoying and leading life to the fulliest when mom and I are pretty much chained to the house because of her PD. Just pondering.

I meant mother in law,not mother.

Move on. Dont you the past as a hitching post. You are stewing over something that happened and is water under the bridge.
This just poisons you and keeps you from living.
Its those you love and have trust in that most times hurt you the most. Step up to the plate and do the best for your Mom. when all is said and done you can face yourself and say : I did my best.
Blessings Virignia

Sounds like a lousy thing they did to you and the hub...such gratitude! Let me tell ya' something...when dealing with sibs, it is never smooth sailing. It is rare in this forum that someone says that their sibs are cooperative and all pitch in equally to help. When it does happen the rest of us just sit here in awe...as if we have seen a unicorn!
Your main focus should still be on your MIL and if she is getting good care. If so, write off the nastiness from your hub's sibs. If not, speak up in defense of your MIL only. Your husband should be able to contact her doc or the NH whenever he has a question. Make sure his name is on the "call list." For whatever reason, your Mom gave the POA to your SIL...who knows why people do anything.
Do what you can for your MIL, visit her often and do not bring up the other sibs, then, forget the rest. Take this time to reclaim your lives. Take a vacation to get away from it all and rejuvenate.