Oh Niffler I'm so sorry that your MIL is putting you through all this BS. Sure, everyone knows she is grieving too, but it's NOT about her. Sounds like FIL and BIL have been tippy-toeing around MIL for too long, she sounds like a spoiled brat!
When my DH passed away MIL/SILx2/BIL created a huge debacle on the day of the funeral, but fortunately (or unfortunately) my mind wasn't on what they were trying to enforce and it all went over my head...so their scenes were totally wasted, although other people noticed and thought they were 'quite strange'.
Spending Xmas alone is not as bad as it sounds, I have done it for many years as it's better than going through all the drama and BS. Sometimes I spend the day in the garden and sometimes I just chill out, but (imho) doing absolutely nothing and just quietly reflecting is what suits me best, and the drama queens can do their thing without including me.
Thinking of you because you've got a double whammy with the funeral and then Xmas, not to mention the other issues. My suggestion is do what 'you' want, you are allowed to change your mind and just say you need time to yourself. Truly I don't think that is being unreasonable in your situation.
All the best for the days ahead and you know there is always someone to 'talk' to on MN at any time.
