I can't see a five item potluck (ie, one item per family), with a significant driving distance and no schedule for who brings what ending well. With larger numbers of people, you have a reasonable probability of variety even with random choices. With four or five, yeah, you're probably going to end up with five salads, or five trays of store bought brownies.
And the thing is, they could host the food without that much effort or cost. They could do the burgers and hot dogs on the grill, stop by Costco for some trays of veggies, big tubs of coleslaw, fruit salad and potato salad, dips and chips. Two litre bottles of pop and iced tea, coffee, ice cream and cookies for dessert. For breakfast, muffins, fruit, juice and coffee.