DP and his ex are both flexible over Xmas. Traditionally DP has DSS up until and including morning of 25th, because he and his family celebrate on evening of 24th anyway (common in France).
Then we drop DSS at his mum's on the morning of 25th, have a drink with them, and leave DSS to celebrate a second Xmas there.
I am the spanner in the works as my family are all in the UK, so it is hard to see them unless they come here, or I leave DP and DSS here and go to UK on my own, or we attempt to do a cross channel flit on the 25th, or we celebrate Xmas on a different day. All solutions are pretty unsatisfactory to be honest, compounded by the fact its hard for me to get much time off work.
DP's ex is so nice she probably wouldn't mind us having DSS for the whole Xmas period, but I feel he'd be disappointed not to see both parents at this special time.
I feel for people who have no chance of seeing their children/stepchildren at all ever over Xmas.