It would be interesting to see the entire vehicle you have there, while the build is in-progress.
Regarding the two controller/motor issue:
When the motors are offground, freely spinning without a load in the air, that can work alright.
The problem is that if the motors aren't physically locked together so they rotate at the same time at the same position, then the controller only knows where the coils are relative to the sensors of one of the motors. This means it isn't putting out the pulses of current to turn the other motor at the right time, and it can cause various undesirable behaviors (including feedback from the motor coils that are in the wrong position relative to their magnets at the wrong time that might be able to damage the controller itself, in theory at least).
You can't tie the sensors from both motors together becuase then the controller will not know the position of either motor correctly.
If the motors are physically locked together at the exact same rotor position relative to their magnet position, so they always rotate in exact sync, then the halls from one motor can be used to detect position correctly for both (because it is now one motor with two sets of coils), and the controller can drive them both directly and correctly.
You can actually use just one battery to drive two controllers that then drive each motor independently, and use just one throttle to control both. If you use one throttle, then use the 5v and ground from only one controller, but wire the throttle output signal to both.
If you need to switch the controllers off independently, then use separate switches for each controller's keyswitch/ignition wire to the battery positive. (or if you use controllers with displays, they will likely have their own independent on/off buttons).
