I am slightly panicking now, and wondering if we should cancel. I wonder if give a better picture of DD8's abilities if it would help people brainstorm solutions.
DD8 has severe quad CP, cortical vision impairment, and some degree of intellectual disability although it's really hard to know for sure with a child who doesn't move or talk, so we presume competence as much as possible. When she is calm, and perfectly positioned, and communicating with a familiar partner, she can use partner assisted scanning and a communication book to tell you concrete messages about the here and now. But that's really limited to messages like "I want my mom" or "I want to go home" or "I like this". She does not talk about things in the past or future, her communication is generally about the here and now. She would enjoy watching a video of a ride, and hearing the sounds and being included in a conversation about them, but she's not going to be able to visually process a youtube video, or my description of such, to the point where it she would be able to comment on whether or not it would be scary to her.
On top of that, even when we know she can access something, there are times when she refuses. For example, there's a park near us with an accessible swing that she loves. To get to it, you need to cross some mulch (as an aside, why do parks get the fancy accessible swing and then place it in a pit of mulch?). About 75% of the time we go, she's excited as soon as she figures out where she is, laughing the whole time she's on the swing, and annoyed if I make her get off to go home or give a sibling a turn. But sometimes, we go and it's really clear she doesn't want to swing which she communicates by frowning and stiffening slightly and averting her gaze. If you ignore her, she'll progress to crying pretty quickly.
Why? I don't exactly know. Maybe her stomach is a little too full from a recent feed, and she thinks she'll be motion sick? Maybe her g-tube site is a little sore, and she's worried about the place the seatbelt hits? Maybe her diaper's wet or she senses she's about to poop and she's embarrassed to be taken out of the chair in a public space? Maybe she's practicing for adolescence and saying no for the sake of saying no? I have no way of knowing, because she doesn't communicate these kinds of things. But, it's really important to me that she knows she has the right to say no, and that we'll respect her messages.
We've gone to a little local park with the family and the same teenage friend we're bringing on this trip, although not since the baby arrived. There is a train ride with seating similar to a bunch of Disney rides that we ride, and we've got boarding down pat. DS17's friend enters first, carrying DD6 (who has problems with her lower body, but is otherwise typical), then DS5 gets on with DS17, and I pass DD8 to her brother, and I board last. If she refuses, then she just stays in my arms, and we meet them at the place where you get off. So that was what I was picturing doing at Disney, albeit with the extra complication of the baby, assuming that people would be able to distinguish between "not planning on riding" and a severely disabled kid who suddenly became upset.
So, what solutions do people suggest? Unfortunately, we're almost certainly going to be staying off site, because I think that the combination of everything we need, at least 4 bedrooms, and 2 accessible bathrooms, plus a kitchen with a decent sized fridge, space for lots of equipment like wheelchairs, high chair, strollers, stander . . . is going to be cost prohibitive on top of 8 park tickets. So that means that solutions like using extra magic hours, or timing things by booking FP+, and character meals perfectly right at sixty days, aren't going to be an option.
I really don't want solutions that involve splitting up all the time. We'll do that some of the time, but being together as a family is kind of the point of vacation, IMO, so if we can't do that we'll just figure out another plan.