DH spend Christmas with MIL because she pressured him to
You husband is an adult, he needs to stand up to her, or maybe he actually enjoys spending Christmas with his parents and siblings and it's you he needs to be honest with.
Either way, I could cope with a hubby who wouldn't stand up for himself.
Its your husbands fault he wasn't there when your grandfather died, your anger is aimed in the wrong direction,
You sound really bitter, I'm not saying its unjustified, it just sounds horrible and I'm sure it's not nice for your husband and won't be nice for your 20month old once they are old enough to understand.
It sound petty that you won't do every other because she didn't (you sound 10years old).
No, you shouldn't "have" to do anything you do not wish to do on Christmas, sometimes in marriage, people compromise in order to help their partner out.
One day Every other year is the most fair way, IMO
Would it be an option to book to eat out on Christmas Day so everyone could attend ?