It only seems fitting to ask family members to bring a "covered dish" or something to help with the food prep. You could offer cake, coffee and soft drinks, paper products. Sometimes when we get people involved, they behave a bit better. Perhaps making a "thing" of it.... 75 different dishes - make your best dish. collect the recipes and create a family recipe collection to celebrate his birthday.
Don't forget to take a family photo. Our neighbors have been hosting the family picnic each year for a long time now. He hosted because his father (90) couldln't travel. Last year it was a long one! 4th of July weekend, but it lasted more like 6 days. People come from all over the country and camped out in his yard. (They get two port-o-potties) Anyway. My husband was a professional photographer at one time. He took my new digital camera and took candid shots and a few of the entire family with Ma and Slim sitting in the front. Well, Slim passed last month. Its the ONLY family photo - I'm so glad we took it.
Attached is a picture of the "tatoo" that was drawn on each guest with a magic marker. They did have such a blast!
I hope your celebration turns out to be a fun and wonderful time.