Your Mom sounds like fun!
Don't burst her bubble and she shouldn't have to change. Nothing wrong with how she does things.
But so, maybe you/your kids and her can open some gifts on the Eve? And on Christmas day/morning.
Just tell your Mom to put some aside, and not all at one time for opening because you are stressed about it... because your Husband's family is very not festive.
But to a certain extent, this is how your Mom/your family has always done Christmas and gifts. So that is your and your Mom's "tradition." And there is nothing wrong with it. I mean, your Husband's family could ALSO be the one to have to "change" their method of Christmas gifts too.
I really don't think, your Mom should have to "change."
What does your Husband think? It is his family that is sort of like not real into gifts. They can be more flexible, too.
I mean, they are going to your house for Christmas day to open gifts... it is your house and you SHOULD have your own traditions too.
They as "guests" should realize that.
Your Mom, is fine.
Don't make the "conflict" about her or make her "wrong."
She is fine.
It seems like, there will be only your Mom (from your side of the family there), and meanwhile ALL of your Husband's family, will be there too. But just because there is more of them versus your side of the family... it does not mean you have to do things, "their" way.
It is your home, and this is your Mom. And you have nice warm memories and traditions of how you gift people, for Christmas.
And that is good. You don't have to be a "Scrooge" because your Husband's family is less festive about it.