It'll be, I imagine, a lot like loading the peoplemover.. (or loading a currently operating gondola). If your party gets split up, it gets split up.. it's not an attraction, it's a what.. 9 minute transportation. People all over the world have figured out how to get on and off these things without incident. I am confident they will do so in Orlando, as well.
I doubt they split up any party that will fit in a single cabin. If you've got special considerations taking up more space like a mobility vehicle, that may split you up. But, that wouldn't be to combine with someone else, but because your party's adjusted space requirement is bigger than a single cabin.
Using the 8 person cabin size, I would guess a mobility scooter and rider counts as 2 to 4 people instead of just 1. As 2 is easy, the scooter has weight and takes up space. Counting as 4 is possible if they raise up a bench on one side. The rider stays on the scooter but is consuming all the space of the raised bench.
For small parties, 4 or less, I could see them combining them if the wait is long. At peak times, combining 2 groups of 4 or less to get closer to 8. Even 4 groups of 2. Maybe a group of 5 and 3 (or 2).
But, even at peak, once a group get's to 6 people, my bet is they get their own cabin all the time.
Not at peak times, when the line should be really short, my bet is every group gets it's own cabin.
Strollers fitting in somewhere between not mattering at all and counting like a mobility scooter if they are huge. Two of those large jogging strollers and you're probably getting you're own cabin no matter the crowd. A couple of umbrella strollers not mattering at all.
