That's a tough ask, Virginia.
Windsor and Greenwich are only 32 miles apart, one basically due east of central London and the other basically due west.
The only route basically equidistant to the south is the A23, the Brighton Road. I spent many years as a child in that area and there are few villages or small towns in the A23 corridor before the M25.
Banstead is a small town west of the A23 somewhat near the M25 junction 9 and maybe you can find a B&B near there. But it is somewhat closer to Windsor and correspondingly further from Greenwich, and Greenwich will in no way be an easy drive from there. In fact, driving south of the river can be really quite challenging at most times.
All the places you listed are easy to get to by train from most places in the greater London area, and by car much more difficult:
Windsor Castle is a very short walk from either of the Windsor stations. Parking is very very difficult there. I once spend an hour trying to park to show my brother and his daughter over from the US the place and gave up.
Greenwich has several stations and is also on the DLR, so very easy from anywhere in London, but has awful parking. Greenwich is also hard to get to by car, there is no easy route from most places.
Dover could be reached by car from Surrey by M25, to M26, to M20. Traffic can be challenging. Dover is easily reached by trains from London, including the high speed Javelin trains.
Stonehenge can be a decent, if long, drive from Surrey, and you can get reasonably close in the car park. Trains from London Waterloo go to Winchester from which local transport is available.
What sort of villages or town did you have in mind for where you wanted to stay?