The doctor is supposed to be the Nurse's superior, but he sure doesn't act like it. The Nurse controls him in every way possible. This is because the doctor is weak and easily manipulated. It's easy to see he lacks confidence and has a low self-esteem. This is perfect for the Nurse because she can run the ward the way she wants without having to answer to the doctor.
The three orderlies, the Black Boys, are all angry, violent people. They are the Nurse's assistants and are more than happy to carry out her ruthless, mean spirited, and often violent orders. They are ideal for the job because they enjoy flexing their power over the patienets, just like the Nurse.