Your wifely duties include supporting your husband -that's interpretation. Think of it as allowing your best friend to lean on your shoulder while he's dealing with one of the most hurtful losses of his life, and having to support one of HIS friends that is very difficult (Mother) -Not an easy task for him AT ALL. So when he's extra snippy, extra intolerable, EXTRA rude, EXTRA snide, EXTRA kind to her and seems to be snappy with you? Just remember he's off balance for the moment and it's not really him - it's a version of him that doesn't know HOW to please the two women in his life that he loves most. The key to it all for you is being the woman in that picture that allows him his space, realizes this and just lets him have his moment for the other woman no matter how unbearable it will be. Loosely put - be the bigger woman, zip your lip, smile and nod a lot, and punch the poop out of a lot of pillows but on the outside? You have the demeanor of a princess and never EVER let the paparazi have an ENquirer front page photo moment with ridiculous caption like HNR having meltdown over news that husbands lover is Bigfoot.
You ARE a princess - go and behave like one. And as far as your mother in law? Just be sympathetic, slightly aloof, helpful to your husband.....and not necessarily FOR her....but him. Do things when HE asks you to - not her. Allow her to have her little boy, one last time - and I think you'll see it will be better for you all the way around. NOT normal (nooooooo) but in this circumstance from what you have described? Either play second fiddle for a few days for his sake and yours....OR get into a powerstruggle and have yourself, HIM and her all living in an uproar. This is a battle that no one will win. Think of her as a sick old woman - and let that play in your mind every time you see her. Sick.old.woman. I am a princess helping my husband. No photo ops here. Always a calm demeanor. Placid as new snow. Deep breath in - and out.......smile...smile.......(get the the hotel?) KILL THE PILLOW.....and breath.
THen leave and just know ------you really did all you could to not give her an inch. Her brain is always on auto pilot looking for that inch.....you gave her nada.