Wow, you have some specific needs that are not all that usual. I can see why it's difficult to decide on the type of RV you want.
I don't know what kind of budget you are working with, but it might very well take a remodel of an existing trailer to meet your needs. In the older Airstreams, the twin bed models have the widest aisle way, but don't usually sleep 6 people... The twin beds could be turned into bunk beds to sleep the 4 kids, leaving the two adults on the front gaucho - which is a long way to the bathroom... and RV bathrooms are not actually built to be comfortable for anyone, let alone for someone with mobility challenges.
I would suggest really reading through the forums to find the good and not-so-good with different models (eg. rear end separation on longer 70's models) and to see what reno's others have done successfully. Here's a link to a previous discussion on this: http://www.airforums.com/forums/f161...irs-14463.html
Your budget might dictate how many options you have. Some people have done complete gut and remodels of trailers rebuilding them the way they want, but it's safe to say that can be expensive.
The good news - many people using this forum are filled with knowledge and good ideas!