Start with the route, not the ticket
Tell your operator how far you can comfortably walk and whether uneven surfaces, steps or long queues are difficult. Ask them to confirm the distance between the legal vehicle drop-off and your intended viewpoint, not just whether the monument is described as accessible.
Confirm vehicle and mobility-aid details
Share the folded size of a wheelchair or walker and whether you can transfer into a passenger seat. A standard car, a local mobility aid and a wheelchair-adapted vehicle are different arrangements. Ask for the confirmed vehicle and any equipment hire in writing.
Keep a simpler backup plan
Give the Taj Mahal its own time block and treat a second monument as optional. Ask where rest breaks and restrooms fit. If the planned route is too demanding on the day, agree with your guide what can be shortened or replaced.