My brother called the cops on me when we physically fought at our house. Do I need a lawyer for this?

If the State picked up the charges you will definitely need an attorney. Your brother doesn't have any control over whether the State pursues the charges, at this point. There are things he can do to help resolve the case favorably, that can be discussed with your attorney. His regret and unwillingness to testify MAY help you, but the DA's office can still pursue the charge. The sooner you meet with an attorney and discuss these issues the better able he/she will be equipped to help you resolve this in your favor.   Best of luck.