I know this is such a sad time for you. I agree with the pp and with your girlfriends who have advised you to focus on what you need this week, and not on what the in-laws will or won't do or say. I do think that people tend to err on the side of saying nothing instead of saying "the wrong thing" so don't over-interpret their silence.
If you need to cry, do so. Do not try to pretend in order to "protect your kids" or out of fear of ruining their Xmas. It's okay to be sad when someone we love is gone, and I believe kids can handle that truth. Stuff happens and we can't drop a bubble on Xmas, and the kids won't be horribly scarred if this Xmas is not the most festive. Mama is grieving her mama. That's important too.
(I lost my brother several years ago the night before Hanukkah started, and every year I light a memorial candle for him the night before the holiday begins. I talk about it with my daughter, and she understands that I am sad about his loss). As time goes on, you will find ways to incorporate your mother & her light into your holiday celebrations. But this year, it is as sharp as it's going to be, and you just need to let yourself feel how you feel.