Database Design (how to handle subclass & superclass)
I've just recently answered a similar question here. What you want is a People table containing data common to all people contained in your DB with other subsidiary tables providing the additional data unique to different roles some of those people play in the operation of your service. The linked question and answer should provide the details you need. If not, a couple of my answers to related questions can be found here and here. However, perform a search to get a variety of answers from other contributers. I have found many times that the best answer for a particular situation may be a combination of techniques from several sources.