I don't know what the terrain is like that you are contending with. Are there obstacles such as steep narrow paths, narrow bridges etc. These days most farmers and ranchers with such needs would opt for an ATV but I suspect that would be much to obtrusive for your application. A golf cart may work but would be limited in the kind of terrain it could handle.
An electric wheel chair could be easily modified by extending the frame forward 30 or 40 cm and fitting larger caster wheels to improve stability and enable it to negotiate rougher surfaces. Because many people who rely on wheel chairs are sensitive to jolts and excessive vibration, damping with one of the shock absorber systems available for mountain bikes would be very desirable.
The trail such a chair would have to navigate would have to be leveled laterally to avoid excessive leaning to either side for comfort and safety.
Electric wheel chairs are not cheep but pre-owned chairs are often available and there are often organizations who are delighted to help fund accessibility plans.
For large groups I think I'd go back to an ATV or small tractor pulling a wagon to those areas that are appropriate. Viewing stages and binoculars may help and would make the experience more real than video cameras and monitors.