How to run two motors on the same button?

[GeeTwo]

You could also use two PWM ports for the two motor controllers. Just send the same command to both controllers at the same time (OK, one immediately following the other).

Note that neither of these methods mean that the motors will be synced. They will just be on at the same time going the same direction. There is always a bit more drag or oomph on one side than the other. If you need them to move together, use a mechanical means to keep them together, or install encoders or potentiometers so you can track them both and slow down the faster one so they go together. (You can also speed up the slower one if you aren't going full speed, but just slowing the faster one doesn't involve the edge case.)