We had our vegan family here today. One of the children is extremely allergic to all dairy products, eggs and sesame, which was why the family all became vegans after she nearly died as a baby after going into anaphylactic shock when given cows milk formula. One of the parents has recently been diagnosed with celiac condition so has to have gluten free food. Not a fad, a medical need.
We also had other family members, some omnivores, some vegetarians and one who is on a slimming diet.
It was not difficult to feed them. The children had Linda Macartney vegetarian sausage rolls (which are OK for vegans) with plenty of veg. For the adults I made a chilli using soya mince, onions, garlic, fresh chillis, tinned tomatoes, tomato paste, veggie stock cube, soya sauce and tinned kidney beans which we had with plain boiled rice and salad. The slimmer skipped the rice and had lots of salad. Everyone seemed perfectly happy and no-one lectured anyone.