There are two main factors deciding whether the two motors (of the same type) will work together. There is the loading - meaning the props in the water (matching size, shape, pitch, water flow caused by hull shape for both), friction in the shafts (bearings etc), alignment of couplers and friction in the motor. Then there is motor efficiency - strength of magnets, rotor to magnet gap, "goodness" of windings and condition of brushes. If all are exactly equal, no problems. Provided the conditions are "near enough" equal, then a bit of rudder trim is the answer.
