Are there lots of you for Christmas dinner? I do about 10 different vegetable dishes so it's more of a kind of vegetarian feast with a "side" of turkey and sausages wrapped in bacon for the carnivores (and a veggie cocktail sausage version too). You don't really need a specific replacement for the turkey.
The kind of things I make are: roast potatoes, duchess potatoes with chives, Yorkshire pudding, sweet potatoes with orange juice and marshmallows (sounds terrible, I know, I made it for a joke for a Thanksgiving pot luck supper - turns out it's amazing, I get asked to make it every year now), cauliflower cheese, chestnut and wild mushroom bake, roast parsnips, carrots glazed with maple syrup, sage and onion veggie stuffing balls, ratatouille, sweetcorn with peppers (fresh not out of a tin, although that is where I got the idea!), crushed peas with spring onions and chilli, red cabbage with apple and walnuts, green beans sautéed in lemon and garlic with finely chopped pine nuts, stuffed baby marrows or aubergines, mushrooms in garlic and cream, little Padron peppers filled with crumbled feta and garlic breadcrumbs on top, and good old, traditional sprouts. You can also add some chopped cooked bacon afterwards as a garnish for the carnivores to things like mushrooms in garlic and cream to make them a bit more enticing for non veggie fans.
They are all things that are quick to prepare, most can be prepared in advance ready to pop in the oven, and you can scale them down and cook in very small amounts (I have lots of small square Pyrex dishes, the kind you might use for an individual cottage pie, and tapas dishes, you could use small disposable foil pie cases if you don't have small dishes). But if it's just a few people and none of them will eat the veggie dishes, that isn't going to work.
My algorithm is, not counting roast potatoes, stuffing or Yorkshire pudding, one different vegetarian dish (an individual pie dish portion) per person. Most people like to taste most things (a spoonful) and take a larger portion of their favourites. I then scale up or down the dish sizes based on likes and dislikes of the guests.
It sounds complicated but actually it's no more hassle peeling 2 carrots, 2 parsnips, one sweet potato, chopping a handful of mushrooms, than it would be preparing a lot of one vegetable for one dish.