If they do seem uncomfortable with your role as their boss, you might need to have an explicit conversation with them about their reservations. Avoiding the subject will not make it go away. If you do confront them, do it in a way that's not accusatory or threatening—by saying, for example, “I get the impression, I could be wrong, you're not comfortable with me as your leader. How can I help you? What can I do to help make this situation work?”
