Actually, I have little idea!
Perhaps sell 3 other resellable shares (at £750 each), and then the annual costs (perhaps £400 each for insurance, MOT and the battery hire). There's no tax to pay, or fuel costs. Then any maintenance can be paid for by ratio of miles driven by each partner. Biggest user pays biggest share.
For practical use, find a really simple asset-share site such as
Share Timetable ? Free Online Resource and Appointment Scheduling .
Because of the type of car, it'll only ever be used for short, local trips - so should be very rare that there will be a clash of needs...?
Interested?