*Thinks about what I have eaten for dinner in the last week*
(lowdown: I'm a veggie, mum's a pescatarian, so is my boyfriend and dad eats meat. In our house we've been cooking 3 different meals since about 1992!)
Macaroni and cheese (parents were having fish pie, so dad made double the white sauce)
Thai red curry (Quorn with curry paste, coconut milk and rice noodles)
Pizza (own ingredients on pre-made base)
Indianish curry (this was a whole family meal)
Pasta with pesto, sundried tomatoes and vegan meatballs
Stuff like zis. I'm not big on salads. As others have mentioned, tweaking meals to fit around your folks will help. Like with the mac n cheese, half of that was already being made and the oven was on.
The curry is a weekly family thing after my shift on a saturady. Dad has organic beef or prawns, mum has prawns and me and Leo have Quorn 'chicken' or tofu, but we have same sauce and sides, just separated out to prevent meat and veggie stuff being put together.
There are plenty of things that can be converted from meaty to veggie, like the curry above, or chilli with rice and tortillas....just separate the portions and add fake meat/beans/veggies to the basic tomato sauce.
Also (god this is now long....) if you can cook, cook something vegetarian for your whole family. If its delicious, it may encourage them to cut down on their meat-based meals each week and a. reduces the amount of meat eaten (healthier, kinder etc etc) and b. makes you not feel so much of a food outsider.
My Dad now only eats meat/fish about twice/three times a week, like how they did in the old days, because he's seen how good vegetarian food can be.