Just be doing a bit of research about this. I didn't realize there was such a vast variety of chairs and scooters available.
Looking at some disability sites - one problem is the highly variable needs people have -some can't use a forward steering column, for example. So it might be difficult to get a one-size-fits-all solution. If I were a care-hire company I'd be inclined to look at the issue and decide that only a specialist centre could cater for the range required.
According to the UK Government website, airlines are now required under the regulations to carry electric wheelchairs etc for no charge provided that the batteries are solid-state or can be sealed. This seems to me to an excellent bit of enlightened legislation.
A lot of modern mobility scooters will disassemble and fit in a car boot.
I know it's second best, but my suggestion would be to locate a taxi firm in Corfu that has at least one suitable vehicle for carrying scooters and chairs, and offer a guaranteed booking service. Also I'd be inclined to check up on the facilities for the disabled at Corfu airport, and if necessary kick arse. Then there's the slight matter of charging points - but that surely must be easy to organise; if a car/bike company could offer over-night charging for a modest cost, this would look nice and friendly, and not need vast capital expenditure. Or you could provide external charge points at properties.
But you've probably done all those things already. Keep us posted!