Can you tell us a little more?? Does Grandmother drive (safely)? Is she 60 or 90? Is it possible she needs you to make the appointment and drive your Grandfather to the doctor's office? Why do you feel he needs to see a doctor?
Grand, if the doctor is ill, is there another doctor in the practice that your Grandfather can see? Or am I reading your posting wrong? If so, as geewiz had noted, we need much more information.
It is good of you to be concerned. We'd like to help, but we'll need more information.