The bridge rectifier to change from AC to DC to run the motor is fine.
As you have a PWM controller, it would be a good idea to add a smoothing capacitor to the input of the PWM controller. The capacitor needs to be rated at 50 V or so, and should be about 5000 µF for each amp that the motor draws.
You cannot connect the outputs of two PWM controllers together, and certainly not in different directions.
I suggest that you find some 24 V relays. They need to be two pole relays, so that they have two contacts that switch at the same time. Wire the coils of the relays to the output of the bridge rectifiers. Then connect the motors to the controllers though the contacts of the relays.
That way, only the active controller is connected to the motor.
28 V rectified is probably nearly 40 V, so if these run for more than a minute or so your relays may get a bit warm. You can add a resistor in series to reduce the voltage but the value depends on which resistor you use.