When I had to cook for a large group that included vegetarians I did most meals buffet style.
On taco night I'd have a big bowl or fajita veggies, then different options for protein. Beef for the real folk, fake meat or tempeh for the veggers
On pasta night I made a big pot of sauce, meatballs for the meat eaters, faux meat balls for the veggers. I had shredded zuchini as pasta (as did the vegan) while my family had real pasta.
stirfry over cauliflower rice - tofu for the veg, meat for rest
Ideally, it would be nice to find dishes both could share, but unless your willing to sacrfice protein intake thats not really an option.
do they eat eggs or fish? obviously that would make it a great deal easier.
good ingredients to work with would be avacados, sweet potatos, coconut.
good luck! sharring is caring