You'll only need ONE 8" fan for that setup - placed at the Beginning of the chain pushing the air (That way if you have any leaks in the system - you wont be sucking dirty air to your exhaust
Also - why not butt the rooms right up next to each other and use ONE A/C ? Vent air using a cheap blower into/out of each room to exchange air !.
I actually do BOTH of these tricks in my Mother/Cloning/Veg rooms.