Tell us more.
What kind of motors ? Do you know the type, or can you make a photo of it.
If you tested them for reverse rotation, that doesn't mean they are also manufactured for that.
Do you know the voltage of the motors ? Can you measure the stall current ?
How do you want to control them ? With speed control in both directions ?
To control a motor with speed and direction, a H-bridge is used.http://en.wikipedia.org/wiki/H_bridge
There are many shields for the Arduino with a H-bridge, but some of them are only for 1 or 2 motors.
If you only want full speed in both directions, the DPDT relay could be used. That could even be used with a PWM output of the Arduino to have also speed control.