I don't think you can count the 17yo boy as a child! He may well eat more than an adult at that age.
My approach would be to get in bread and jam and cereal and milk and croissants etc for breakfast; quiches and cold baked salmon and eggs (for omelettes) and baguettes for lunches; then plan out dinners (as you have).
THEN, I would buy an absolute fuckton of fruit, raw vegetables, snacks, yogurts, olives, cheese, peanut butter, crackers etc. You will all eat much more than you think over the NY period, especially if you're lolling about indoors, especially with bored teens (who at a push might make some toast or a pot noodle).
Crisps, juice, nuts, wine, beers, milkshake/hot chocolate, bananas, apples, chocolate, satsumas + satsumas + satsumas, olives, cornichons, Bombay mix - just loads of that stuff.
THEN I would make sure we cook and eat all the perishable stuff there (spinach, meats, fish, raw veggies that can't be kept, milk etc) and then share out whatever's leftover for people to take home.
Sounds fun!