I'm very sorry for your loss. It's particularly difficult this time of year--when my dad died 12/22/95, I spent the month saying, "Merry F-ing Christmas!" Out of character for me, but it was how I felt.
I know it is a very difficult time for your family, but try, try, try, to at least put aside your feelings for yoru MIL until after the services, for your husband's sake. Some people are just in denial--when my godmother (my dad's sister) had cancer, my dad didn't mention it until she died. All my cousins knew, she was in treatment for months, but Dad thought she would get better, so why worry me? I felt so awful at her funeral. Also, when my grandmother was hospitalized for "routine pneumonia", my dad put off visiting her since he thought she'd get better. Well, she died, and again, we weren't at all prepared, even though my uncles had said, "Come now!" My point is, some people are just like this--my dad had many, many good qualities, but he could live in a state of denial like nobody I've seen, bless him!
Right now your job is to be the loving, supportive spouse that your husband needs. Feel free to blow off steam here as needed if it helps you to give your family the love they need the other 99% of the time. This will get easier with time (not the MIL issues, you're probably stuck with them, but the overall situation).