[Alan Anderson]

Doubling up window motors might end up with a worse problem. If one of them runs just a little faster than the other, they'll start fighting each other, and the anti-backdrive feature is likely to lock one of them up. If you don't need the motors to actively hold their position against a force trying to move them, it might be best to open them up and remove the pins.

This application probably calls for a stronger motor, though. It's a good opportunity to do the math and find out what torque is required at what speed, then match that to an available motor and gearbox.