Don't run different subs.
Different subs have different specs. Even in separate boxes they will cancel each other out and sound like complete ass.
Sell all the subs, and buy 2 matching, good quality 12's.
Guarantee it will sound 10x better than 5 mismatched subs.
Don't run different amps to the subs.
Different amps have different power outputs and will end up powering each sub differently which will cause more cancelation.
Sell the 4 amps and get 1 good sub amp.
Question for you now, the 5.25's are speakers correct? Not subwoofers? If they ARE speakers, I would suggest eventually trying your hand at fiberglassing your door panels to fit 2 5.25's per door.
Any other questions, feel free to ask.