Lady blackmailing to marry her otherwise will file false rape case

You are explained two facts, 1. She was a affair with your brother; but she concealed that she is a married woman or now divorcee. 2. She threaten to your brother that if he is not solemnizing marriage with her, than she will be registered a false criminal case of rape or she will be committed suicide.
You submit a representation to the concerned senior police officer; vide which you will be made a request for taking an action against that lady for your unnecessary harassment & threat given by her and also request to protection of your life and liberty for that lady; because apprehension is there for registration of a false case. if she has already been made an attempt to committed suicide than you have liberty to file a criminal complaint against her; before the competent court having jurisdiction. You have also remedy to file a petition before Hon`ble High court for you protection.

You can file complaint to police, mahila mandal with regard to blackmailing. But before doing it collect all the information with regard to her litigation with her husband. Plz consult a lawyer before filing any complaint. Thereafter you can also move to high court seeking protection. For detail discussion you can contact.