[Russ Beavis]

Excellent question - do motors in parallel add their torques?

In the simplest case when both are perfectly stalled, their torques should indeed add.

Once the motors start turning, however, one will inevitably start to dominate and things will go askew (possibly also due to gearbox efficiencies). At that point, you'll need to carefully model the rotor and load inertias, gearbox efficiencies and differences between the motors and drive electronics.

Russ