Jessica, you shouldn't feel the need to make your parents believe in ghosts, nor should you try. People come to believe what they believe for a variety of reasons: they were brought up that way; they want to believe; they've had an experience that compels them to believe.
But to me "believe" might be an inappropriate term when it comes to ghosts and the paranormal. When people ask me if I believe in ghosts, I say no. Belief implies that there is no evidence; that you're accepting something merely on faith. However, there is evidence for ghost and haunting phenomena. No one knows exactly what that evidence (experiences, photos, videos, etc.) actually represents, but it has certainly been part of the human experience for all of recorded history across all cultures. So I don't "believe" in ghosts; I think there is compelling evidence for the phenomena that is worthy of continued and thoughtful research. Belief is not required.
Chances are, you wouldn't be able to convince your parents that there is something to the ghost phenomenon. They would either have to have an experience themselves or read the volumes of information on the subject and consider that conclusion.
It's always good to be skeptical, but equally important to be open-minded and to consider and evaluate the available evidence. Blind belief is as equally worthless as blind skepticism when it comes to the paranormal since neither brings us any closer to understanding the true nature of the phenomena.