Sister Misguided Parents and ripping them off since long

I am NRI and my parents have always been living with me. I started working in India since 1992 and continued to work and live the same place till 2006. During 1997 to 2006 my parents were staying with me and they were highly biased towards my sister and keep her helping secretly. During these period I have to stay many rented house and I have been managing the complete show rent and all expenses. My father retired in 2000 but still living with me till 2016. In 2007 I came abroad with my family but keep visiting them once or twice a year and kept them in my own house. In the mean time I always keep helping them financially also. The way my parents advocating my sister it always keep me in doubt and My parent always keep on fighting with me to support her daughter. Recently my dad expired, but spent quite a lot of money for his treatment and I tried to settle my mother at different places. But again my sister keep her misguiding and asked her to harass me on making false sickness etc. and I have to bring her to the same city. Now when I was back to abroad after making all her arrangement, My sister managed to get her at her home. Now my sister has prepared my mother to complaint against me at post office that I have snatched her all pass book and id. However, I am the only son and I wanted to secure her money and hence got a bank account opened in her name. All bank and post office account were joint account (Father & Mother). On going through previous pass book of my father there are certain transaction which create doubts that my father had purchase house for her. My parent have always kept me in dark misleading me as they don 't have money and at the same time they keep on helping my sister. Now my mother is with my sister and there is no way to communicate my mother, this is like hijacking my mother and keep separating with me. My sister already have allegation in court for money fraud. My mother is illiterate and got so impleaded that she keep on saying that I will live with my daughter. I know my sister is greedy and once she will my mother's money my mother will be in trouble. Is there any way legally for the following: 1) Put the money on hold / dispute when my mother should not get money from post office 2) Due to misguiding by my sister over 20 years, my parents always hate me, my wife and my children despite many good thing done by me as part of their responsibilities and always keeping them in comfort. On the other side they love my sister and their children. My sister has always been showing my parents that she does not have money etc, and keep taking their sympathy and money. This was completely false act by my sister. 3) I believe apart from ancestors property, Me and my wife has the right on managing parents property rather than married sister. Appreciate your help.