hi O.P
has PP has just stated best place to go is Disabilities board.
can your dad walk on a moving conveyur belt for a few seconds and step onto a moving platform?
if so he wont have to stay in to ride, if he does need to stay into ride, you will need to advise the CM of this at the time, they will transfer you to a manual wheelchair to board a special ride car which can accomodate the chair, only a few rides actually can do this, best thing to do is head to the town hall in MK and pick up a disability accessibility map which advises which of the shows have wheel chair access.
also for parades, on that map it will have a icon for the places with special roped off areas for scooters and chairs however you can watch the parade from anywhere, justy turning up nice and early and grab a spot.
have a fab trip.