Parking is laxly controlled on St Lucia and unless you cause an obstruction or leave your car somewhere for more than a day, you are unlikely to encounter any problems.
It’s really only in the capital, Castries, where you might find you’ll have to pay parking charges. Elsewhere free parking is readily available.
As we’ve noted, it’s unlikely you’ll encounter enforcement of parking restrictions, mainly because there aren’t really any of note. It’s only if you park inconsiderately that you’ll encounter enforcement.
There are no concessions for disabled drivers, mainly because they haven’t been deemed necessary. If you really can’t find suitable parking, stop and ask a local for advice and help. There’ll usually be some way in which your needs can be accommodated.