I have a 2017 Doblo 'car', which is a wheelchair adapted vehicle, but I'm guessing it has the same door mechanisms.
Inside, there are handles, above the trim panel, ahead of the windows. Those handles have little triggers on them, which must connect via cable to the lock mechanism, including the catch at the bottom of the door, that holds it open. (last pic)
Logic suggests that you should be able to add handles and cables, to facilitate internal release of the doors. Confirming a list of parts could be tedious, and expensive, but finding a scrap 'car' to provide the bits could be a good option.
Hopefully this is enough, as I do not really wish to remove my door panels, as they are currently undisturbed since build.