Crimes are prosecuted by the District Attorney. They are not prosecuted by the victim. Therefore, your brother has no power to drop the charges and the D.A. can go forward with the case even if your brother tells him or her that he is not interested. Your brother's cooperation can be important, or even critical to the D.A.'s ability to get a conviction at trial (depending on whether there were any other witnesses to the event) and these cases are often dropped if the victim does not appear to testify. However, if your brother finds himself under subpoena, then a refusal to appear and testify can have consequences for him and he should consult with an attorney before making that decision.
You can reach Harkess & Salter LLC at (303) 531-5380 or info@Harkess-Salter.com. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.
The decision whether to prosecute or not prosecute a case is made by the prosecutor's office. Your brother can certainly contact that office and indicate that he does not want you to be prosecuted, but he is not empowered to "drop" any charges.