In all honesty people do -not- have to have meat at every meal and they won't starve or anything like that. I'm vegan for ethical reasons so there's no way I'd bring meat or animal products into my own home.
I agree completely. If you have gone to the trouble of cooking up a lovely spread, your family should be grateful. It's not at all offensive to serve an entirely vegan or vegetarian feast - it's not as abstaining from meat for one meal goes against their morals.
They eat meat out of preference where as you don't eat meat for ethical reasons. (but it's a good idea to find out if they have any allergies and never never lie to them about what's in their food.)
It's entirely acceptable for you to politely decline meat at their house. But for them to decline your food, or bring their own meat would be rude. It would be like saying "hey I know you spent ages making me this three course meal from scratch, but I'm gonna bring mcdonalds and eat it in front of you, because that's what I like." Very rude. You wouldn't go to a dinner party and leave brussels sprouts on your plate because you don't like them.
I really think you have to go all out and show them that they're not missing out on anything though!
Stuff that I like to make for holidays includes... herb roasted veg, potato salad with veganaise, punk rock chickpea gravy from vegan with a vengeance, home made biscuits, pumpkin seed crusted tofu with home made cranberry sauce, maple glazed green beans, orange glazed beetroot, mashed potatoes, stuffing. I've had good results with home made tofurkey - my relatives loved it.
For dessert - the most important part! gingerbread apple pie, pumpkin/sweet potato pie, pecan pie, home made vegan ice cream/sorbets, chocolate orange mousse pie, ginger cookies, oh and strawberries dipped in melted dark chocolate (I live in the southern hemisphere - summer christmas! strawberry season!).
ARGH now I'm getting excited. I can't wait for christmas... I freakin love to cook.