Translation:The parents are the mother and the father.
Is the gepatro just patro with a prefix? If so, are there any other words that use the prefix?
Yes, it means both sexes taken together and is therefore plural. It can be used with any word which can refer to both sexes together.
So does that mean that if my parents were homossexual, I would refer them by saying 'miaj patroj' or 'miaj patrinoj'?
I suppose it would depend on whether you meant your legal parents or your birth parents ... but yes. Absolutely.
"Chris and Pat are getting married in the fall" is difficult to translate if you don't know who Chris and Pat are.