Would greatly appreciate a recommendation to accommodate a half or full day tour of Athens for 4 people in May. One of us has limited mobility (uses a cane). Prefer van pickup and return at hotel.
It all depends on what you want to visit and your friend's walking ability.
Most archaeological sites such as the Acropolis, Agora, etc. are located in the same almost entirely pedestrianized area, so a van service will be useless.
The Acropolis is a hill, with steps and slopes to access the Parthenon.
The Anafiotika neighborhood in Plaka is also mainly crossed by small pedestrian streets with slopes or stairs.
Hop-On Hop-Off tourist buses only travel along the main avenues without going near these sites.
So to be as close as possible to the places to see and avoid walking, find a hotel in Plaka.
There is handicapped elevator access to the Acropolis.
Check maspero.com but I am not sure that a person using a cane would be qualified as handicapped enough to use this elevator up and down.