I am making a few assumptions here.
Assumption #1: Your pork butts average 8.5 lbs and your packer briskets average 14 lbs (these weights are what my sources provide).
You should calculate a 45% loss in weight in cooking both types of meat. (this could vary anyplace between 40% - 50% so I use 45% as an average).
Assumption #2: You will serve 6 oz of brisket and pork to each person. (this is a LOT of meat so there could be a fair amount of meat leftover)
Using these numbers you can expect to produce approximately 41 servings of brisket and approximately 75 servings of pork. Therefore your 2 packers and 6 butts will produce plenty of meat for 40 people. If food costs are an issue you could cut the number of butts down to 4 and that should still yield approximately 50 servings of pork.
For the sides I would suggest one pan (equivalent to a full size steam table pan) of each.
6 - 8.5 (butts) 34 lbs raw less 45% cook loss
(6 X 8.5 lbs) - 22.95 lbs = 28.05 lbs net cooked pork,
28.05 lbs x 16 oz = 444.80 oz divided by 6 oz = 74.8 servings
2 - 14 (briskets) 28 lbs raw less 45% cook loss
(2 X 14 lbs) - 12.60 lbs = 15.40 lbs net cooked pork,
15.40 lbs x 16 oz = 246.40 oz divided by 6 oz = 41.07 servings
Hope this helps.
Do I smell SMOKE?????