DC Motor PWM Circuit Implementation
In order to properly select a motor for a load and select a controller for the motor, you need to know the rated motor current, the current that the motor can safely draw continuously. The stall current is only tolerable for a very short time. Some larger motors can not tolerate stall current at all. A good controller should limit the current. Larger industrial motors controllers commonly limit overload current to 150% of rated current for one minute and have an instantaneous shut-off at 200% to 250% of rated current. That is probably a reasonable objective for your situation also.

The linked controllers have over-current features to protect the controller, but I did not see anything that would protect the motor. Something like that would be ok for careful operation as a learning experience. Set the speed to zero and connect the motor before connecting power. Turn the speed up slowly and up carefully. That will keep the motor from drawing too much current. Check the current with an ammeter. Operating the motor at 25% of locked rotor current will probably prevent it from getting to hot quickly. With out a specification from the motor manufacturer, you will not be able to determine. How much the current it will tolerate without overheating or what temperature it can withstand.

Two motors are usually not connected to one controller, but it is ok to do that as a learning experience.