Conflict between staff

I work in a 20 bed NICU. Our supervisor recently resigned because family reasons, but come to find out a group of girls have kind of taken control in the NICU and go above her head if they don't like the answer that whe gave them. She has been gone 2 weeks and these 4 girls have taken over many of the responsiblities of the Supervisor. It has been a living HELL in the unit. They are doing the schedule and causing conflict amongst staff. They, of course, are blaming the last Supervisor on some of these decisions. These women also don't like to work very hard when they are at work. In the last 2 weeks I have had many run ins with them. Sent 2 emails to the Manager of the floor, who is suppose to be running the show somewhat, but she has the whole floor, 3 departments. I have met with her twice and she is basicly backing thesse women. I need to be more assertive and speak my mind to them and tell them to stop. At what point do they get in trouble, when should she get involved and speak to them? Why do I have to do her job? We are loosing staff weekly because of them and their decisions. When does the Manager put a stop to it? Any suggestions on how I can approach these women? HELP!!!!