I have one of my flower tents (4x4x6.5') connected to a veg tent (2x4x5').
A 6", 630CFM inline filter/fan pushes air out of the flower tent, and passively sucks the air from the veg tent through its cooltube with 6" ducting. The far side of the veg tent lamp has a short piece of ducting with piece of pantyhose over the open end to catch debris, the other side exits the tent via 6" ducting through a ducting vent, and is left open in the bottom of the flower tent through one of its vent ports.
There is enough draw with the exhaust fan in the flower tent, to cause negative air pressure in the veg tent as well as the flower tent.
The exhaust fan runs 24/0 at its lowest speed setting, and keeps the veg tent from overheating.
I'm unsure however, if one 8" exhaust fan will be able to handle four 4x4' tents.