I like the themed meals for dinner. I would do:
All Breakfasts: cereal, oatmeal packets, toast, eggs available for ppl to cook, and maybe a batch of muffins. Basically this should be self serve.
All Lunches: a big pot of soup, crusty bread, grilled cheese, sandwich items, cold pasta salads (can be store-bought or made ahead).
Afternoon cake: I would buy some nice store-bought cookies, or you can prepare cookies in advance buy making different cookie doughs, then freezing them in dough balls (on a cooking tray in the freezer, then transfer to a big freezer bag). Each day, you just plop the frozen balls on a tray and cook it up for the group. I'm not British tho so idk what expected of afternoon cake...
Dinners:
1: Italian, lasagne, big salad with dif veg and a nice dressing, garlic bread.
2: Meze/med night: hummus, tzaziki, eggplant dip, a nice red lentil soup (check out NYT Melissa Clark recipe), falafel (pre-made), flat breads, Greek salad, and a big pre-made Greek spanikopita. this could all be mostly pre made stuff if you're stressed about the cooking.
3: Bean Enchiladas (check out budgetbytes.com), guacamole, salsa (premade), corn chips.
4: desserts: big tubs of ice cream, popsicles for kids, more cookies, fruit.
Other suggestions: buy a ton of crisps, crackers, snack items, and fruits.
Also maybe switch out one of the dinners for homemade pizzas, you could buy the pre-made doughs, have pizza sauce, shredded cheese and veg topping options.