What to do at a formal party of all ages?

for my 16th birthday party i am looking to have a formal get together at a nice place and serve appetizers and possibly a small dinner. the party is going to be a benefit to raise money for the american cancer society. i will have my friends, young cousins as well as grandparents there so i have no idea what to do there. i don't want it to be boring but i would rather not get a dj because i will have my grandparents and aunts and uncles there. HELP! keep in mind we will all be in dresses or nice clothes!