Threatening and blackmailing for fake rape case

Hello sir Recently, my brother informed me that he is being threatened, being given death threats, blackmailed and forced to quit his degree buy a person who happens to be the brother of a girl with whom he was in a relationship. When he first met this guy around one year back in among his friend as everyone was joking around he also joked about himself saying that is belongs to a millionaire family, following this date, they guy and and his family started to come close to him, my brother continued to maintain what he said because he believed saying anything otherwise will impact his relationship coz he fell in love with the girl, when they came in a relationship they had a consentual sex and both Continued their relationship, but recently when the brother of that girl got to know about this he started blackmailing and threatening my brother to the point that he even gave him death threats and forced him to quit his college and he is calling him to meet alone. He has chat proofs from the girl where she said that my brother didn’t raped her, they had consensual sex when his brother was not around, and that she didn’t told his brother when he asked whether it was mutual or not. What should my brother and we do to save him from this.