OP I posted this on another thread where a poster was worried about cooking for 12.
This is my "plan". As you can see I have no issues with cutting a few corners (like bought in roast potatoes, even though I can cook them well myself). Key is prep as much in advance and think about how you can re-use some things i.e. Cook one serve twice.
Like you OP I'm cooking for 12 this year as I do every bloody year but in my case over Boxing Day as well and 27th also.
I've pretty much much got it nailed now. We don't eat until late 6pm Xmas day so the in laws can go to church locally before they travel to us.
Ok my plan this year:
Christmas Eve:
I'll cook a large ham and soup and cauliflower cheese.
In addition I'll be cooking a vat of cock-au-vin
Then I'll cook a curry for me, DH and the kids to eat that evening. I double portion and freeze half.
I set the dining room table.
Christmas Day
I lay out the ham, plus some lovely pate, cheese and deli items on the kitchen table for everyone to nibble on and help themselves.
For the main event I'll serve the soup I made as a starter.
Controversial I know but I don't do turkey. Firstly I don't like it and secondly it's all the pfaff of the the trimmings that's a pain (stuffing, pigs in blankets, cranberry/bread sauce etc).
I will be cooking a huge rib of beef which looks spectacular but also means I can forget all those fiddly trimmings. I'll serve it with roast (I'll be buying pre-prepped ones cooked in goose fat) and mash potatoes (I'll cook double of the latter), the cauliflower cheese I made before, glazed carrots and broccoli - plus lashings of red wine gravy that I'll make with some bought in stock.
There will be xmas pudding and a bought in posh chocolate dessert option.
Boxing Day
I'll cook an English breakfast to fill everyone up.
Then we'll eat again around 4pm (so I get to skip cooking lunch and dinner)
This will be the cock-au-vin with jacket potatoes. So all I have to do is re-heat the chicken, shove some potatoes in the oven and cook some green beans.
We will have cheese and biscuits (left from the xmas day deli spread) for dessert.
27th:
Bacon sarnies for breakfast
I'll make a chicken and ham pie with the left over ham (and bought in pastry) and serve it with the rest of the mash I made on xmas day, plus some broccoli.
Pudding I'll probably buy in something like and apple pie and custard.
Then.....by 8pm when everyone has gone I'll open a well deserved bottle of champagne 
For the next few days we will survive on leftovers and curry so I don't have to cook anything!