Lot of variables here, like how many woman vs men, how much time allowed for the meal, any other food being served, is this a well dressed group, or a a casual dressed group, mostly young vs mostly older, heavy vs slim? My best guess would be 2.5 person per slab depending on how the variables play out, or 3 to 4 bones per person.
why not cut your loses and cook whole untrimmed slabs, cut up, then you may get away with about 3 slabs less, and less to deal with.
Lg Spicewine on trailer
Weber charcoal grill
2 ugly drums, semi retired
Bbq toolbox, formerly Chargrill smoker
My wife has gas, its a Brinkman.