Jerry, dear me, how awful! I'm so sorry for this situation, especially happening right smack in the middle of the stressful season. I hope your FIL makes a quick and full recovery, and I hope there aren't any other casualties in the family in the meantime.
I have one sanity-protecting phrase for you: 'Well, time for our long, brisk walk! Coming, dear?' This assumes that your MIL wouldn't want to come with, but where there is already tension in the relationship, PLUS the holidays, PLUS an upsetting medical crisis, it can only help to get some fresh air, exercise, and distance. (Remind your wife that you do eventually need to turn around and go back.)
I'm sending some pixie dust your way

that all ends well, and soon.
Well, shoot. I came in here to wail about eating my own MIL's fresh-from-the-oven very special Christmas cookies, and the headache they gave me, but this trumps cookies. Okay, I thank you for the dose of perspective, and hope that Christmas finds you in a settled-down and in-law-free home. Take extra good care of yourself right now and give your wife a big hug -- it'll do you both good!