I imagine anybody actually living in these homes had to install a false floor to at least give them something level to put their stuff on. Bookshelves might have been modified to sit level if they were up on the lip of the bowl as well.
Either that or the homes came complete with custom furniture that fit the odd shape of the home, and the owners just had to content themselves with their decor being forever stuck in the 60s.
I suspect there are many reasons why these homes are sitting abandoned and decaying now.
These seem closer to RVs than homes to me. There is no apparent space for beds (do the chairs fold down?), no kitchen, and not even any closets. I guess you can do whatever you want in the interior, but the lack of space and the strange shape is going to make anything usable difficult. I couldn't even tell if there was a full shower in that museum model's airline bathroom thing.