All drums are different as are butts.
That said. I get shoulders two to 15-16 lb pack. I prefer bone-in but often boneless is cheaper, go figure.
Two packs give you 4 8lb butts. I run my drum at 275-285 and they'll take around 9 hours to cook. In the desert heat you could easily run your drum in the 300 range and not have to stay up all night. A wrap at the stall definitely speed up the process.
No matter, possibly the best que your guests have ever eaten.
Pete-my first UDS,a brick pizza WFO, a leaky Chargriller offest, wifes Weber Genesis gasser,a Lightening Fast RED Thermapen, new baby Traeger