Mathmom included my favorites.
I keep thinking how hard it is to cook for vegetarian (a vegan would absolutely made it difficult for the 18 others!!) as well as someone Kosher. I've juggled the 2 my whole life.
I'd start with vegetable dishes--stir fried, in quiche--or pasta dishes with veggies. Meat or chicken cooked on side. If someone really Kosher, they would need special meats/ckn, and separate pots for cooking. Are they Kosher-style? Enchiladas and omelets cooked to taste are great. Salads of all kinds, where one adds-on
Mathmom--wish you were around to offer cooking class for the novice. Caltech: PA 16: Cooking Basics