The very first time I tried to use my
ECV on a bus, there were three people who refused to get up who obviously were causing me problems in getting the ECV where it needed to go. The driver told me they can't ask anyone to move. I too felt like crying.
Two ideas:
(1) Bc of that experience I was totally spooked by the "old" type buses and wanted the wider buses (which I now know cause others problems! but they are easy with a
scooter than can be backed on). I learned (from a lovely ECV user who I ran into -- not literally! -- on a boat to MGM) that I could call Guest Services at my resort re the problem and and they would actually route a bus to pick me up at a specified time to take me to my desired location. I was an an Epcot resort, and as this seemed to be an "extra" bus, it wasn't crowded. I didn't think of calling Disney Transportation directly, that seems easier. Once you are at the parks, you are fine as those buses will be empty when you return to your resort and you will be boarding first. As an aside, I ended up on the "old" buses again and was fine, but I agree with the others, those few moments of just plain RUDE behavior stuck with me. I truly think that if you call and explain the situation they will help you.
(2) remember that you can put the ECV into freewheel so if a family member can help, they can just push the ECV into position if that is easier than driving it on.
(3) If you or another family member takes the scooter on, you could simply say, "excuse me, the scooter needs to be loaded in a special spot, could you please allow me to get it there?" If you wait for people to move they can ignore you and pretend nothing's happening but if you say something you call them on it and they have to either move or say something pathetically rude which hopefully they would be too embarrased to do. I freely admit that this is a fantasy scenario of mine bc I wish I had said something to the people who were sitting in my way staring at me with the whole rest of the bus empty when I had my problem.
I am truly sorry that your family encountered such clueless people. TONS of pixie dust for the rest of your trip.

Cupcake