As many as they have the time to.
That much food would feed at least 102 people.
I would make 15 -16 pounds
The number of people 64 briskets can feed depends on portion sizes and the context of the meal. Generally, a standard serving of brisket is about half a pound per person. Therefore, 64 briskets, assuming each weighs around 10 pounds, could feed approximately 1,280 people if served as the main dish. However, this number may vary based on side dishes and individual appetites.
15
i would say about 100 chickens to feed that many people.
One chicken for 3 people = 183 chickens.
base on a standard portion of 4oz per person it would take 10 pounds to feed 40 people at that rate.But if you like to have a second portion for say 20 more people I would recommend 30 pounds.
120
I would use about 20-21 depending on size
If they are having 1/2 eact 25 chickens or if 1/4 each 13 Chickens
Chickens eat bugs on the ground if they are free range. Many chickens are living off of a grain as chicken feed.
The US Department of Agriculture (USDA) does not allow poultry farmers to feed hormones to chickens, at least to those destined for food use. (see the related link)