Here "rise up" means to stand up in court and speak against someone to a judge. AT: "must not speak to the judges about something bad that a man did" (See: [[rc://en/ta/man/translate/figs-idiom]])
Here "mouth" represents what the witnesses say. It is implied that there must be at least two or three witnesses. AT: "at the testimony of at least two or three people" or "based on what at least two or three people say happened" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-explicit]])