DP has an old friend who got together with a friend of mine a few years ago. They had a DD (now 6yo), but the relationship didn't last and they now have their DD more or less 50/50. It's his year to have Christmas with her this year and he's asked DP if they can come to us. I feel a bit weird about the thought of spending Christmas with my friend's DD, when I imagine it'll be quite hard for my friend to be away from her daughter, and possibly in her own, over Christmas. DP thinks it doesn't matter as my friend won't be seeing her daughter on Christmas day whether or not his friend brings her to ours.
Is it makes any difference, they'll probably come around lunchtime (ie not be here in the morning for presents etc) and maybe stay over the night. I'm not that close to my friends these days (see her maybe 3-4 times a year), but her ex is a close/old friend of DPs
YABU = It's fine, seeing them at Christmas doesn't make any difference to anything
YANBU = It'd be insensitive/weird to be with your friend's dd on Christmas when she doesn't get to see her