Are wheelchairs available there for the elderly or disabled? If so, is there a cost to use them?

Yes wheelchairs are available however it is on a first-come first-serve basis. The Smithsonian museums have a wheelchair program to assist as well. Select the link - www.nmaahc.si.edu and click on Accessibility at the bottom of the home page for more information.

Yes come early they open at 10:30 and ask for a guided tour

I really don't know the answer that. We came with our own travel scooter. But it looks like Keisha did a really good job at answering your question. 👍 I didn't even know that the option was there!?!?🤨