What is the best car SUV town car impala and keeping in mind ease of access to the passenger seat to rent if I am taking a paraplegic relative with me?

I assume you are looking for a full size car or SUV/minivan? Access to the rear seats is the same in most minivans -- not great unless you are able-bodied. SUVs tend to be high off the ground and this can present problems, also.

In terms of rental cars generally, I would suggest a PT Cruiser for its passenger and back seat room and ease of access. It's close to the ground and the doors open wide. A full size car such as a Mercury Grand Marquis, Buick Lucerne, or a Chevy Impala would also have good passenger access and a spacious interior. A car with leather seats may be easier to get in and out of since you won't have the issue of "my butt's stuck to the upholstery".

Try going to the lot of a rental company and ask to check out the cars they have currently. Usually they will be more than willing to assist you as long as they are not too busy. Try going on a Monday or Tuesday morning, as these are less-busy days.