I'll give this a shot. According to SoEzzy's catering planner, if you had 4 3.5# chickens, cooked weight would yield 75% of total uncooked which is 10.5#. This is figuring 4oz portions.
This may be bone weight with, but I would go with 6 to 7
I am sure somebody else will chime in and let ya know for sure.
BabyGotBack BBQ team
Uber fast stealth black thermapen
Cubby blue Thermapen
22.5" weber X 2