Answer:
I believe that a person must be moral to teach morality to others. Take, for example, an analogy to sports: if a person has never played soccer their whole life, but perhaps they've read a bit about the sport, there would be nearly unanimous agreement that the person would not be able to teach how to play soccer to others, since they have never done so themselves. Why would it be any different for morality? That is why a person must be moral to teach morality to others.
“For the things we have to learn before we can do them, we learn by doing them.” - Aristotle, The Nicomachean Ethics