Most camping cutlery sets consist of 16 pieces: Fork, knife, spoon and tea spoon, suited for the average familiy of four. You might consider buying a set for 6 people to have a little reserve.
Inexpensive cutlery sets are made of 18/0 stainless steel, higher standard cutlery is 18/10 stainless steel. We test our camping cutlery ourselves in the holiday! In general, all camping cutlery is dishwasher-safe, so you can use them even at the garden party.