There is still a whirlpool tub in the "master" bedroom, even in the fully handicapped units that have roll in showers. The floor plan is basically the same, it's just some of the things like sinks, toilets that are different.
If your father in law doesn't need the things like raised seat toilet and grab bars, you can just get a regular unit. They are roomy enough for a wheelchair to get around. As someone else mentioned, not all the first floor rooms are handicapped accessible.
According to an email I got in response to a question to MS last year:
"There are 19 studios at Old Key West that are Handicap accessible, 19 one bedrooms, 20 two bedrooms and 1 grand villa. These are the rooms with the roll in shower."