Hi Breanne ~
Walt Disney World does a great job of providing
services for Guests with Mobility Disabilities. There are some attractions that your Dad will be able to remain in his scooter (ECV). For other attractions, he may need to transfer from his ECV to a manual wheelchair or be mobile to board. There is a list for each park found on the link above. If he needs physical assistance when transferring, someone in your party will need to assist him.
Most of the queues can now accommodate ECVs and wheelchairs so you can all stay together. There are some attractions where ECVs and wheelchairs parties are separated in order to accommodate as many Guests as possible in ECVs and wheelchairs. Once of those that comes to mind is the Walt Disney World Railroad. Guests in ECVs must transfer to a wheelchair and that seating is in the front of the train. One person may remain with your Dad and the others will have to sit in the general boarding area.
Handicapped seating is in different places in different show venues. A Cast Member will be able to escort your Dad and your party to the handicapped seating areas. Depending on how crowded the venue or area is they may only let one member of your party sit with your Dad and ask that the other members of your party sit nearby. A lot of times, it is in the row just in front of them so you'll all be close.
Most of the buses can usually accommodate up to two ECVs or wheelchairs. If there are other Guests in wheelchairs or ECVs waiting, you may have to wait on more than one bus. For those Guests in ECVs, they ask that they transfer to a seat if possible. We can usually get to board at the same time as my son so that we can all be on the same bus.
I'm limited in space but please feel free to visit again with all of your questions. We are hEAR for you!
Wishing you minnie magical memories :-) Allison V.