Property distribution

Hello sir, This is in regards to the property which my grandparents own. My grand father has two properties on his name and today both my Grandparents has passed away. They have only two children a son and a daughter (My father and my Aunt). Father 64 - retired state govt. employee with no source of income and Aunt - 51 divorcee. She got married in the year 1986 and was divorced after two years. my aunt has no children right since from the day of divorcee to till date her whole living expenses (food clothing, shelter all were borne by my father. Instead he asked her to stay at one property on her own. Now she has sent a legal notice to my father demanding for a share in both the properties ( 50% in each) or to name one property completely on her name. This has happened because my father has asked for half the rent where she currently stays, for his medical expenses since he is not able to afford his expenses. My grandfather didn't write any will nor did share any property on any of their children. My question is does she has the complete right on both the properties or we as grand children to our grandfather has any right to claim for the property, we are three children to our father two sons and a daughter,. all are married. we as sons has very low income (private employed both) living together along with our father. My sister is staying along with her husband separately. Please advise us in detail about the share in both the properties, as my father is fierce with the legal notice from a lawyer he received. He is ill and recently got with a major diagnosis.