Husband wants to leave me because of his brothers mrg nt working

I and my sister married to same family who are 2 brothers. my sister and her husband's marriage is not working as he claims she has an extra marital affair. and my husband supports his brother saying my parents knew of my sisters affair and still have hidden the fact from them.I was with my parents for studies.I used to visit my husband in Bangalore during vacations. now my sisters husband wants money and gold to give divorce to my sister and to allow me to live with my husband ...before also her husband used to harass her to bring her before marriage money earned by her and surrender it to him. We hav a recording of the same.I didnt have any problems with my husband till date..and he wants to leave me bcoz of his brother. and his brother also misbehaved with me when I went to live with my husband after studies and removed me from his husband told me to know ad he will calm his brother and bring me back .but later involved with bro and doesn't allow me to live with him. and says to give the money to his bro then I can come to live with parents told him to go for mutual divorce and let me live with my husband but they cant give the money and gold to which he is not agreeing and says he wants money then only he will give mutual concent divorce otherwise he wont allow to let me live there. I have recording of the call where he asks my sister to bring that money.and even of the call saying he will kill me if I come there. Whenever i try to talk to my husband he says its my parents fault if they surrender themselves by giving tgat money his brother will allow us to live.he asks me to kill my sister or file a case against my parents for their property then he will live with me. He is not ready accept in frnt of all that he wants to leave me as such he has no reason to leave me . even if they prove my sister deserted his brother can my husband leave me?isn't it a blackmail by using me in their mrg matter, wat legal steps can I take?