South Pacific countries generally have poor facilities for disabled travellers. Wheelchair users will find getting around a problem: footpaths (sidewalks) can be patchy or nonexistent, domestic planes have steps and narrow doors, ferries may not have ramp access... Some larger international resorts offer rooms with disabled access, but it’s not common.
That said, South Pacific cultures look after their elderly, disabled and infirm as integrated members of the community – there are no special schools or aged-care facilities. Islanders won’t simply look away if you need some help to get into a taxi or up some stairs – they’ll rally-up some helpers and pitch in.
Get in touch with your national support organisation before you travel to enquire about the countries you plan to visit.