Might it not be simpler to use one motor and gears? If there are two separate shafts, 1:1 gearing will do the job. If co-axial, it needs either two layshafts to get the reversal and return to the outer shaft, or a belt and one layshaft.
I have heard that some ESCs can tolerate driving two motors. Just running flat out, there shouldn't be a problem as long as the controller can handle the amps, just reverse any two of the wires on one of the motors, and it will run in reverse with respect to the other.