Rent dispute

The house in which i live is in the name of three brothers. My husband and two elder brothers. His second brother died in 2009. After his death the rent which was earlier shared by three brothers was divided between two brothers and sister in law . This continued for 6 years until recently when we learnt recently that the 1/3rd share of the rent which my sister-in-law was getting was supposed to be divided between mother and wife of the deceased. Here I would like to mention that my sistet in law does not have any children. She is doing a govt job. She has a seperate house of her own and getting her husband's 50% pension.She also got all her husband's dues for ex GPF,insurance etc. My mother -in-law is a 80 year old widow. She is completely bed ridden. Her only source of income is the widow pension she is getting. Pls suggest if she should get 50% of 1/3rd share of the rent. There are lot of expenses being incurred on het medical expenses. My eldest brother in law is visually impaired and the rent he gets from the house is his only source of income. My husband is retired and his source of income is too from the house. He does not get pension. We all live in a joint family. We too have no children and i am a house wife. My sister in law does not want share 50%rent with my mother in law who is ailing for quite some time.