a note about parks - If the members of your party who need it get a GAC, it can allow them to sit in the front row of shows. I know in theatres, if you are of short stature it can be very difficult to see over the seat in front of you. that can be very helpful. I don't know about any other GAC accommodations that could be helpful - that depends on the person. Also, with the wheelchair, both of them will be allowed into the wheelchair viewing area, which will allow them to be able to see shows and parades more easily. I am short, only just reaching 5 ft recently (and i am 24!) and I am about 3'5" in a wheelchair, so I have some idea of how hard it is to reach things and see over people (though I do not claim to understand all their difficulties!)
The boats are generally quite accessible, as long as the water level is not very high or very low. I have never had a problem