I took a 6 week solo road trip across the USA last year so you'd think I would be able to give some tips. But mostly I don't have much.
On my trip I hit many cities and sights including New Orleans, San Antonio, Austin, Carlsbad Caverns, the Grand Canyon, Disneyland, Yosemite, San Francisco, Reno, Salt Lake City, Manitou Springs, St Louis, Chicago, Niagara Falls, Ottawa, Montreal, Bar Harbor and Boston.
I think your hardest part will be finding rooms for 5 people that have a roll-in shower. Most of the rooms I had were a king-sized bed instead of 2 twins/queens. That worked fine for me since I was alone but for your family of 5 that would be a problem.
I had all of my hotel rooms booked and confirmed as accessible before I left home. I knew where I would be sleeping each night, what cities I would be visiting on each day and I had a good idea of what to do in each city. For me having it all planned out was best. Plus I'm a planner so I had a lot of fun planning the trip.
Overall no specific hotel chain stood out as being most accessible. I stayed mostly in Holiday Inns, La Quinta and Marriott brands. Some were better then others but it was mostly just luck of the draw on the hotels. It seems most hotel chains do not have a standardized format for their handicapped rooms instead the room is whatever was in style when the hotel was built.
Wait I just thought of something!

Get an Access Pass to the National Parks. It's a lifetime pass given to those with disabilities that allows free or reduced admission to all of the National Parks.
http://www.nps.gov/fees_passes.htm
Anyway, if you have any specific questions I'd be glad to answer in any way I can. Have a great trip!!!!!
Also, here is a link to the blog I kept while traveling. It's not really centered on access as much as what I did that day.
http://billsears.liv...al.com/?skip=40
http://billsears.liv...al.com/?skip=30
http://billsears.liv...al.com/?skip=20
http://billsears.liv...al.com/?skip=10
http://billsears.livejournal.com/
Edited by BillS, 17 July 2010 - 06:30 PM.
Just a regular guy making his way through life.