Have nibbles ready for their arrival - especially the teenagers. Bags of crisps/tortillas to empty into bowls, and some salsa, tub of crème fraiche or sour cream with chives snipped into it, and hummus, tend to work well for dipping. I usually have plenty of carrot and celery and sweet pepper sticks for dipping too.
Big pot of curry or chilli, or a few large lasagnes are always great for catering in large numbers. Thai red curry can be nice and made mild. Spag bol is usually eaten by everyone. What I often do for large groups is cook rice for everyone, and then serve 2 options - a spicy dish (curry or chilli) and then a creamy dish (chicken and mushrooms in white wine and cream sauce, beef stroganoff etc). Spicy is not too spicy, but should appeal to lots.
Alternatively, a buffet of a side of salmon portioned up (or just steam darnes of salmon altogether - soooo much easier both to cook and serve already portioned up), with a tub of crab claws and a tub of prawns used for garnishing (and eating), and some lemon wedges, is nice. Or platters of cold meats - but while that's do-able, I tend to avoid that one, as I never have enough leftovers and don't feel like cooking more joints (although supermarkets/delis will do them for you, and often present them already sliced up).
Garlic bread or just fresh crusty bread sliced up (butter beside it for those who want it).
A couple of big bowls of salad - a mixed leaves, tomato (cherry tomatoes, or cut up large tomatoes), coleslaw, potato salad and something like broccoli and hazelnut or grated carrot. Maybe 3-4 salads in total. And a dressing on the side.
If you are not asking others to bring deserts, I'd suggest:
A large bowl of mixed berries or fruit salad
A bowl of jelly (ostensibly for the kids, but lots of adults tend to dig in too!)
Bowls of whipped cream and ice cream
Perhaps a plate of meringues (plain, to put together pavlova type deserts as pleased) or an actual pavlova (but then don't overdo the fruit bowl) or a roulade thing
When catering for SUCH large groups, we tend to not bother with cheese course, but if we do, I have 2 boards going around.
Tea and coffee, with a large box of chocolates (after eights, or we like Butlers chocs in our family, or Leonidas if someone has been particularly nice in the purchasing Department!!).