Christmas as the in-laws
Have your in-laws asked how Santa works or just assumed you are going to follow how they did Christmas and Santa when their son was child.
in my family and the way I have always wanted to do it, Santa brings a set of presents only from him to the house where you are sleeping and only to kids.
My in-laws tonight have told me 3yr old, Santa will be delivering presents to their house for her. I'm annoyed at this is this isn't how I want her to think Santa works, and I don't thinks it's as magical.
Apparently all presents are from Santa too even if they have name from other people, which I also don't think is right.
I'm now dreading Christmas afternoon with them, as I think the way they have said tonight is going to ruin the magic of Christmas morning
I would just say to them that's not how it works in your family. Santa goes to your house and the rest of the gifts are from family and friends. Easy. Just talk and make your point. Also, have the partner speaking with their parents so they know how it works in your family and that they need to stick with it