There are 2 sets of 4-pin headers. They are wired in parallel to allow you to easily just connect two pre-wired motors. You could accomplish the same thing if you wired all motors together by twisting like colored leads and plugging them into a single header. Generally speaking, parallel wired steppers maintain equal but lower overall torque while series wired motors maintain higher torque, but torque lowers as speed decreases.
I think you're asking for all sorts of problems trying to drive 4 motors in sync with just a ramps board. If you were going to be able to get away with it, you might try wiring two motors in series, then each pair in parallel. Or better, but not great would be to use E1 (the 2nd extruder connection) to drive a pair of motors in parallel or series, and then z-axis to drive a pair. Marlin supports this in current branches. Not sure about other firmware.
I think a better solution (although likely to require menchancial reconfiguration) is two double ended steppers each driven by a dedicated controller, or possibly 1 larger single ended with belts or a series of shafts to interconnect all axes.
