Twelve is a lot to have leftovers for though, and if they're there later as well that would be the 'cold' meal wouldn't it?
Jen's is a good compromise
How about a big gammon joint (we can get great big ones in the market, good value), either Jen's veg idea or new potatoes, or a big tray of Boulangere potatoes (nowhere near as rich as Dauphinoise).
Plus - red cabbage? Personally I'm not keen on the usual long-cooked with sugar, vinegar, apples, whatever, but that would certainly work and can also be sitting in the oven.
A couple of years ago I discovered you can also cook it a 'normal' amount of time, then toss it with creme fraiche and paprika, and love that
Also they're all things that can be just put on the table - gammon sliced of course.
Shepherds pie would be nice, base can be made ahead and frozen (or indeed the whole thing) and only needs one veg.
Fish pie?
Or a casserole, which could also be made ahead and frozen - venison or beef in red wine? Jacket potatoes for the least effort, or mash.