Getting pedals that are bi-directional without distinct front & back is one solution for tandems.
If you have pedals with distinct left and right sides, they can still be used. You keep the left & right pedals where they are, but swap the pedal axles to make them fit the cranks. So on the front crank, you put the right pedal-axle on the left and the left on the right so they can thread into the cranks correctly. Then on the rear, get one more right pedal-axle for the left pedal.
Due to the improper thread-directions, you'll want to use some blue Loctite on the pedal-threads to make sure they don't creep lose.