Guardian for sisters property?

According to my mother wish i have done my sister marriage with a person who she liked, but after marriage broken his promises which were he made about taking care of my sister and he took her for seperate family in my native. While the time of my sisters delivery he got married with the another woman who is his relative..and he was managing the two families for some time and later matter got serious with sister and another woman, husband made mental torcher and slow my sisters husband took her gold and he skiped the matter. After few months, my sister told me that he is not coming home properly, not taking care of her, he was telling lies and enjoying life with the another wife. My sister came to know all this and got illed with the disease Anxiety Disorder. I (brother) brought and gave treatment for 1 year and now she is better. He (sister husband) never visited from past 1 year and now he came and telling that i surrender myself for my mistakes, but i need my wife n daughter. Problem is my sister is innocent handycapped, he was secretly talking with sister in my phone and he brain washed her and telling i can manage both wifes. I asked about how u manage n its illegal he says " i don't want to give explanation to you (or) anybody i spoke to my wife she is ok with me now. My Grand mother registered the Agriculture land 1 acre to my sister, and my father registered the 20 Anaknam land to my sister, and wrote a WILL (veelunama)of House (cost of 40lakhs present). Now, what he saying is give my wife property now ? I will takecare of my wife, nobody needs to worry. And he is not at all talking with me. What ask help - Is there any law that my sister should not sell property by listening her husband words? Is there anything i can be guardian without selling property and take care of sister daughter future, that nobody should sell that and handover it after she is Major? Please, help out of this so that my sister daughter should not suffer and my sister should not become medically ill by losing everything. I'm worried because i took care of my Sister and daughter from past 5 Years - Her Delivery, Medical treatment, Daugther care n studies everything till yesterday she was with me, now she went with her husband by saying - " Anna, dont worry i will give a chance for 3 months for my husband to take care of me. If he fails i will come back."