|It is great to be friendly with your employees, but not so great to be friends with them. The reason is the exact situation that you described.|
If you want to be truly effective as a manager, you have to act like one. At this point, unless your employees' behaviors are outrageous, there is no need to start counseling or disciplining. Rather, the best approach is for you to meet with them and discuss the situation on a low-key basis.
The idea is to let them know how much you enjoy working with them and how satisfied you are with the team. At the same time, let them know that some of their behaviors are just not working. Be quite specific in describing these behaviors, and then describe some alternative behaviors that would work better in these types of situations. Open the discussion to their suggestions and questions, and be sure to listen carefully to what they have to say.
Be sure to wrap up the meeting with positive expectations. And, down the road, give your staff some positive feedback when you see improvements in their behavior. Managing friends can present problems, but it sure beats managing enemies.