The two primary specs to be concerned with when matching a motor driver with a motor are current and voltage.
For current, look at the stall current rating of the motor you are using, and make sure the motor driver is rated for at least that current (continuous rating, not peak). The driver can be higher than the motor current, but you do not want the motor stall current to be higher than the rating of the driver.
In your case, when wiring two motors to a single driver, you'll want to make sure the driver is rated for 2x the motor current, since it is driving two motors.
For voltage, you want to make sure the operating voltage of the motor is within the range of voltages the driver will work with. You don't have to worry about how many motors the driver will be driving. 2x 12v motors will still be operating at 12v, not 24.