I am no help with dinner as someone in the family always does turkey.
I do brunch on Christmas Day. I can have anywhere from 10 - 20 people. I do have one hard and fast rule, no guests can arrive before 10:00 am.
I make 2-3 wife savers, bacon, sausages, tea, coffee, champagne and OJ, plus a fruit plate.
I do make make ahead mashed potatoes for big dinners. I make up one to two huge lasagna pans of them. Everyone loves them and they taste really good.