So it was a Christmas movie all along

It's random that a family would celebrate Christmas?

It was weird to have Christmas music over the end credits when almost the entire movie had nothing to do with Christmas. Seemed out of place.

It actually ties up the movie and brings closure with the girls acceptance of their childhood home being sold.
At the beginning when they find out the house was already sold, they storm off to the parents new condo to complain. At one point Mora shows them a Christmas elf in which the mom tells her to take it as they no longer need it because they were getting a table top tree. Kate freaks out and says how they cant have Christmas there.
So at the end of the movie they have all settled down and are happy and go to the parents condo for Christmas. And they are completely fine with it.
Mora - It still feels like our Christmas
Kate - Yeah. Cause we're the home