How mobile and how stable are they?
Can they get themselves in and out of a bathtub?
Can they climb up and down a stepstool?
(Getting into the Potter would be similar tho less stable than getting into a bathtub/using a stepstool.)
Is this a conversation you can have with them or are they used to others making things happen? If the latter, are the caregivers coming along? Are the caregivers used to helping with awkward transfers? (Transfering in and out of a boat would be awkward)
Here are some thoughts.
1 - Talk with them about their mobility and limitations.
2 - Check that your insurance
is up to date.
3 - Well in advance of the sail date, find a willing participant, put him/her in a lifejacket, have him/her slip into the water
between the dock and the boat, then grab the lifejacket straps above the shoulders and pull the person onto the dock. Do this a few times. (Dunking them to their chin helps create extra buoyancy. It's surprisingly easy to do this and lift
up someone your own bodyweight and a bit more.)
4 - Now have the wet participant help you retie the boat with the cockpit
caprail as close to the dock as possible. Instead of fenders, use camping closed-cell foam pads to get the boat closest to the dock.
5 - Then have the wet participant do a tub transfer. While standing on the dock, he/she will sit down on the caprail, then swing one leg over the caprail into the boat, then swing the other leg over the caprail and into the boat, then ease his/her seat down into the boat.
6 - Practice running the lines in the cockpit
with people sitting in place. Probably need 2 wet participants to simulate this. Don't expect people with limited mobility to move about during maneuvers. Find the best places in the cockpit for people to sit.
7 - Practice docking
with people sitting in place.
8 - Now have the less-wet participants exit the boat in reverse. Lift
themselves into seated position on caprail (if they can kneel on the cockpit seat and then twist to sit on the caprail this will be easier, otherwise this is an awkward/unstable/full bodyweight move), move one leg out onto dock, then the other leg, then stand on the dock.
Or maybe build a ramp