Responsibility of married daughters

My maternal grandfather have only 2 daughters. He has no son. Both of the daughters are married for last 35 years. The younger daughter is my mother, and elder daughter is my aunt. For the last 25 years my mother take all the responsibilities regarding finance and all other matters of my grandfather, and my grandmother died in 1998. My aunt did not take any responsibilities, and for the last 3 years she even don't contact my mother and do not ask for her father's health condition. At present my father is retired person and he can't take the responsibilities of my grandfather. So my mother want to give some responsibility to my aunt of my grandfather.