DC motor and its weight can carry
The fundamental thing to worry about is Power. Your motor has a particular maximum power output. It has a continuous power output limited by heat dissipation, and a peak power output, limited by the capacity to absorb heat.

Your wheelchair needs power to accelerate it (probably not the limiting factor), power to roll it against its friction (probably not the limiting factor) and power to run it up a hill at a particular speed against gravity.

You can always reduce speed with gearing to allow you to have enough torque to do any of these activities easily.

The design skill with a vehicle is to choose a gearing so that peaks like acceleration 'feel' performant, and that max weight up expected hills 'don't feel sluggish' with continuous power output.