Holland America line also has a good reputation for their service to elderly disabled passengers.
Have been on 2 Fred Olsen cruises and I think it would be difficult to imagine a cruise line that puts itself out quite so much for people who are elderly and/or less mobile. There are lifts, cabins with disabled access and loads of people whizzing around in wheelchairs/scooters etc. They also apparently go way beyond the legal requirements in terms of medical staff on board.
Thomson Cruises cater for the disabled.
The Thomson Celebration & Thomson Spirit both have 4 cabins aet aside on deck seven for the disabled, in which the facilities are very wheelchair user friendly.
I know this because I cruised on the Celebration last year with my disabled brother and you are able to get ashore to visit the sites apart from when there is a tender to shore.
I don't know whether there are care facilities on board and therefore recommend that you contact the tour company.