The fact that you transport your grandparents from time to time and it's easier for them to get in and out may be a benefit. It may be easier to get your three dogs in and out of the car. A real estate agent may need to show multiple houses to a family of four. Stress benefits to your customers over and over in your letter and in your brochure. Use the power of a third party to re-enforce your message.
Chances are they have.
We are much more comfortable trying something is we are familiar with someone else who recommends that product. Many products use a spokesperson to deliver the selling message. We may not actually know the famous movie star but we often feel that we do. And, if we like the person we may very well buy the product based on the testimonial of the star. In small towns there are stars too.