You want to add a second e-motor by using a front hub motor? Yes you can. I would use a thumb throttle on the left grip for the front motor.
-You will need to add a second 48v20ah battery pack, or whatever the hub motor requires.
-I didn't see a brake on those hub motors. If they have no hub brake in them, you will need to rig up a rim brake from a mountain bike or kick scooter.