For a wheel chair, limiting the options to ready made drive systems that you can obtain used for under a hundred bucks, in under a couple of hours you could have a little kick scooter mounted on the chair underside. Ditch the front end, but keep the rest in tact. That, or bolt a golf buggy unit on, which would have lower speed and better traction due to the gear reduction and pneumatic tyres. I can’t see the sense in using hoverboard motors.