Easy things to scale up are:
pre made lasagna and salads
steam or roast baby potatoes, roast Mediterranean vegetables and roast chickens or chicken joints (could do some as Greek lemon/garlic & some plain to cater for preferences)
2-3 big pots of curry (the same, or different ones) with 2-3 big pots of rice, a pile of puppodums or naans, and some bowls of chutney, raita, diced tomato/onion, sour cream or yoghurt (for cooking for any sensitive tastebuds) as sides
Mexican night of fajitas or tacos with all the sides
could a BBQ or other buffet style meal work another night - chicken wings and ribs in the oven, sausages, a mix of burgers/prick chops/lamb chops/chicken portions/kebabs with meat chunks and veggies etc and a few bowls of different salads work another night? You can mix lots of different flavours that way to suit lots of tastes, and keep some plain.
you can add bowl of green or mixed salad and crunchy French breakfast (part baked may be useful) to all of those for people who are less adventurous
Breakfasts - perhaps do a batch of diced fruit one of the earlier mornings (can be eaten as snacks other times), but maybe do a breakfast pack for each house of a couple of cereals, couple of jams, butter, tea/coffee, milk, juice, etc.
One morning could have bacon sandwiches (cook in oven), another could have a couple of pots of scrambled eggs with toast, another fried mushrooms on toast…etc.
Buy in quiches for 1 lunch, another day of sandwiches, one morning you have time to dice the veg do Spanish omelettes, and more sandwiches.
My inclination would be having salad bowl and crusty bread at each lunch and dinner. Bowls of nibble things like olives, hummus with breadstick/carrot sticks, crisps…can also help while cooking is going on or as sides to fill in gaps.
if lots of kitchens, maybe allocate 1 to be salad making, 1 to be veg cooking, 1 to be main item cooking, 1 in charge of sides etc for each meal. Spreads out the helpers too, so easier to work around each other. And if you have limited prep time, are there things you can do ahead - like pre-make the curries/lasaganas, buy ready made, or even prep the veg/marinate meats at breakfast time or while someone else washes up from a meal, to be bagged up in big ikea ziplocs (they do a big size as well as regular size) for use later?