We just got DH's roster for Christmas, and it's absolutely crazy!
He will basically be asleep on Christmas Day to catch up on shut eye!!

Anyway, I will more or less be carrying Christmas Day by myself apart from opening gifts first thing. Does anyone have any suggestions for games, entertainment I can play with the kids?

I got a set of skittles today and I might ask DH if he can find the Bocci set - perhaps some simple party games like Musical Statues? I was thinking of also filling up the paddle pool as it's going to be STINKING HOT and sitting in it with the kids, they'd be sure to get a kick out of Mummy in their wading pool.

I really want to make it fun for them!

I will be grateful for any suggestions to suit 4 y/o twins.

you could fill two containers with white rice and cars for pretend snow play on the sidewalk so it doesn't get the indoors messy...
or have a bush decorating contest/small tree in your yard with homemeade decorations/noodles on strings/etc....
go on a nature/discovery walk and then let them help you use the treasures they find to make a small nativity in a shoe box (lots of imagination needed here!)...
have fun foods for the day that relate to the nativity...say shepherd's pie for lunch, and a king's feast of fruit in the pool for a snack, fun things like that!