My husbands sister and her husband

My husband and his sister are the 2 children of my mother in law. I am married for 20 years now. My mother in law was staying with us only till now. My father in law was also staying with us till he expired after around 4 years of my marriage. Though both of my in laws were pensioners we were only taking care of their expenses. My husbands family always treated me a 3Rd person after marriage. My husbands sister never liked me somehow. After my father in laws death she totally blamed me and my husband for it and said that she will keep her mom with her only. But my mother in law chose to stay with us. That time we were in chennai and my husbands sister was in Delhi. But soon she took transfer to chennai and After coming to chennai my husbands sister totally took control of my mother in law pensions...jewels etc. We never bothered and continued to financially take care of my mother in law. Soon my husband got another job in hyderabad and we moved here. My mother in law also came with us. Though she would often go to help her daughter My in laws always treated me a 3Rd person and not much respect. After over 10 years my husband realised he has to support me to face every situation in family. My mother in law too started liking me slowly but never helped or supported me though. she onlys helped my husbands sister. My husbands sister is an engineer and holds a good position in an MNC and travels frequently even abroad for even 2-3 minthst. Since her son was small my mother in law always used to go to her house .... stay there to take care of my husbands sisters son and cook for her son in law. We also never felt bad. Even after 18 years of marriage my husband or I never knew how much pension my mother in law got or what she does with it. On 3-4 occassions she giftwd us money that we took happily. She gifted similarly to her daughtwr too. We did our duty well only I feel. My father in laws last rites were also conducted well by my husband by spending lots of money and even now he does. But 3-4 years back my brother and his wife wanted to keep me away from my father's property and we had some issues that I openly discussed in front of my mother in law thinking she's one family member. But she shared all this with her daughter and now my husbands sister is not sending back my mom in law and forcibly made a will taking all her monthly pension. Also sold her property and made herself custodian. She's also defaming that we r not taking care of my mom in law. My mom in law is now 79 and she's not in condition to take any decis ion. Whenever we talk she says yes I will come there. She loves her son. But they poisened her against me. My mom in law talks nicely whenever I call her ..or my husband visits. But recently they are not giving phone to her. Half property she wants to give her son. But documents in her daughter possession. I don't want money but want my mon er in law to know we called her. What legal action I can take