no it wont. at half volume you might be surprised at how much less power the amp makes. when i had voltage drop it wouldnt happen until the last 3-5 notches on the volume. at 45, very little drop, at 50 i saw 12v.
OP, what ohm load are you going to run them at? at 1ohm i think you will be ok. half ohm... eeehhhh, no. i mean you could... but i wouldnt like where the voltage would be at.
the 2 battery per amp idea is useless. and i mean that because they will all be connected in some way, they all go back to the alt at least. so you really wont have them separate. SO, you should have them all connected together in the back to help the flow between them.
hope that helps.