10-12 ribs on racks I usually pick up, so 25 racks times 10 is 250 ribs. Let's say for some reason 5 people won't eat the ribs(vegetarians, religious reasons, etc...) that's 250/70, which is 3.5 bones per person and that seems about right. Some will eat more some will eat less, but it's a good average. 18.8 will yield 14-16 pounds cooked(in my experience only), I assume eating them on sandwiches, might be wrong though, 14 pounds with the average sandwich being a third pound makes 42 sandwiches. Just rough numbers from what I have found helpfully to me and take them for what they are worth to you.
Wsm, UDS, Meco bullet smoker, COS, Weber Spirit gasser
Devil made me Q it BBQ team-head cook