The correct answer is 3. Tilting the wheelchair back as it descends does not create an unnecessary safety risk.
Asking the patient to lean forward would likely cause the patient to fall forward out of the wheelchair. The patient must keep their center of mass back so the wheelchair can descend without forward momentum.
The wheelchair brakes must remain off so the wheelchair can roll down the curb.
If you position yourself in front of the patient, they will not be able to tilt the wheelchair backward more effectively manage the wheelchair as it rolls down the curb.