I cater to these specific diets and it's not hard at all. Don't worry....and you don't have to serve mac and cheese every day that he's there. There are tonnes and tonnes of vegetarian foods that you can make easily. They're cheap, healthy and everyone can eat them. Look at simple things like spaghetti, tofu, stir fries, french toast, pancakes, muffins and fruit, eggs and toast....loads of meat free meals. I would suspect that they are likely going to want a reasonable protein replacement with the meals. I've been using quinoa, eggs, cheese, TVP (textured vegetable protein in spaghetti sauce), tofu, beans and lentils, etc. If the family stated that they're vegetarian, I would almost suspect octo-lacto (egg and dairy ok) but ask. Usually, if people are off animal products all together, they'll indicate that they're vegan.....that's a whole other ball game. But gelatin, I believe, is an issue right across the board, so watch for that on your labels. Astro yogourt is gelatin free

If you need a few recipes, pm me and I can pass some along.