You want the combined impedance of the woofers to be the minimum that the amp is rated to drive. That maxes out the potential power of the amp.
These formulae tell you how to figure it out http/physics.bu.edu/py106/notes/Circuits.html
If any of the woofers have dual voice coils you don't have to use both of them.
Using different woofers means that you are mixing the sound of them. That can degrade the quality even if it plays louder.