Vegans coming to Thanksgiving Dinner.. Any main or side or dessert ideas welcome!

Depending on the vibe of the rest of the dinner you may want to do something more presentational; something veggie centric and beautiful is a great idea if the rest of the table will have "company" tableware. I know you said you didn't need recipes but something like the whole poached and roasted head of cauliflower here on food52 is great because it can be carved and looks impressive.

Other than I'll say that when I was a vegetarian I always appreciated when hosts/family members held meat out of dishes when the meat was mainly garnish or subbed mushroom stock when they would usually use meat stock so that I could eat most of the meal. A vegan dressing that everyone is eating (maybe with nuts and/or flax involved for some protien) and just happens to be vegan will make for some very grateful guests.

I've made this in years past, always to rave reviews. Seems the sweet potato or squash route can make for more filling dishes.
Bonus is it makes great leftovers, if you make enough.

I just found this recipe for Butternut Squash "Meatloaf" in the latest Costco magazine. It sounds yummy! And I might make it for Thanksgiving. http://www.costcoconnection.com/connection/201611?folio=39&pg=42#pg42

These are such FABULOUS answers - thank you to EVERYONE for your great ideas!

I'd recommend the mushroom gravy, https://food52.com/recipes/7483-vegetarian-mushroom-thyme-gravy
Just sub a neutral oil for the butter when making the roux. It's a favorite with both vegetarians and carnivores in my family.
Also consider Middle Eastern flavors--'Jerusalem' has recipes for roasted squash and onions drizzled with tahini, and roasted sweet potatoes and figs topped with balsamic glaze and pomegranate seeds.
I recently made baklava for a vegan friend (commercial filo is made with vegetable shortening), using vegan margarine to brush the sheets, and making a spiced sugar syrup to soak it. Add a layer of sautéed apples between the nuts and you have a cousin to a pie.

Shoot...I think my answer wasn't posted.

I see someone already said this but just last night I stuffed acorn squash with sage, thyme, onion, garlic, wild rice, apple, (and bleu cheese and sausage) and then deglazed the pan with bourbon.

The responses in this thread may be useful (about vegetarian food for Thanksgiving, but the majority of ideas are vegan or easily adapted as such): https://food52.com/hotline/33765-vegetarian-thanksgiving

Sauteed Brussels Sprouts, love the crispy outsides. Served with lemon slices to drizzle over sprouts, delicious!

i do a vegetarian thanksgiving every year, but i typically make it more of an "apéro" than big meal, so there are lots of little things.

one of my favourite vegan pieces from this tradition are heidi swanson's sweet potato falafels (http://www.101cookbooks.com/archives/baked-sweet-potato-falafel-recipe.html). they are a bit untraditional, but delicious and easy to make. also, you can make the sweet potato part a day or two in advance.

if you pair these (or something like this) with some vegetable side dishes and a nice salad, i'm sure that will be enough for the vegans. they will be happy you made the effort ! (i know from experience ;) !!)

Don't worry about trying to replace the turkey. A few nice veggie dishes, a salad, and some kind of grain will do it. I recommend 101cookbooks.com for inspiration. Her spiced pumpkin pie recipe is vegan and really great.

I have a recipe from North African cuisine - sweet potato cake with chocolate topping. Vegan. Can be served as is, or with various garnishes...fresh fruit, roasted nuts, whipped coconut cream or dairy cream. If it sounds interesting, I can post it here or email to you.

It sounds daunting at first, but I think you could cobble together a few options that would be friendly for vegans and omnivores alike!
Some thoughts off the top of my head: grain-based dishes, such as farro with mushrooms, kale and/or winter squash. You could also roast acorn squashes and stuff with a mixture of grains (barley, farro, etc.), greens (chard or kale), walnuts and cranberries, which would look festive. There are also some creative preparations out there for cauliflower, e.g. "steaks." A simple preparation of charred broccoli with lemon juice and sliced almonds could also make a nice side.
Many nut-based and chocolate desserts are vegan friendly. Coconut milk is also a good base for desserts that would otherwise be dairy (like pudding).

Good luck!