I agree with Scott
There are no lines, but if you haven't done so, go online right away and get a ticket for timed entry. If there are none available, I would call and explain your situation. The staff are very nice and may be able to help you.
I saw multiple visitors using wheelchairs. The museum uses ramps to move from one level to the next. I believe you can get a ticket ( no charge) for a timed entry.
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