Wait a minute, you going to have 7 adults cooking, or cooking for 7 adults? Because 7 adults is not anywhere close to be a large group, not even medium, not even mediocre. 7 would be considering small group. And it is not much different than cooking for 1. Just multiply everything by 7. Grill hamburgers, have bunch of sides make a self-serving bar, some chips, you are done. Ground meat is pretty cheap so is shredded lettuce and some cheese, sliced mushrooms, maybe some avocadoes.
You are what you eat.