As soon as anyone has a one-off bad experience it's easy to get worried, and the internet tends to melt down and decide the sky is falling.
Seriously, don't let it worry you too much when one person has a problem - but it does remind us that in a resort the size of Port Orleans, sometimes things can slip through the cracks. Personally if so much was obviously wrong from the outset I think I would have asked to be moved to a different room, but the OP was short on time so decided it was acceptable for a few days. I'm glad they are reporting it though, as otherwise any problems won't get fixed. It's far better to report issues while you are there though, but I do understand that they didn't want to waste any of their Disney time on the matter. Suffice to say that their experience is not the norm.
Yes they do, but the elevators are located in the middle sections of the buildings (which are set some way back from the river) so all of River View Royal Rooms, except for a few central third-floor ones, are a bit of a trek from the elevators to the actual room. I would definitely contact the special needs department in advance and get them to put in a request for one of the centrally located River View rooms near the elevators.
The ferry boats are fully accessible, and guests can remain seated in ECVs for the trip.
There is a bus stop (East) not far from Oak Manor, but from Parterre Place it would probably be easier to use the footbridge over to the main buildings and the South Depot.
Andre