Right of married daughter in her maternal grandfather's property

1. My grandfather bought property in 50s. died in 1974. 2. His son (my father )got married in 1976. 3. My cousin ie my father's sister's daughter got married in 1984. Both of them my father's sister n her daughter were staying at my father's place as my aunty was widower. 4. my grandmother died in 2005. 4a. My single uncle died in 2013 w/o any heir. 5. My aunty who was staying at my father's ( grandfather's house) house also died last year. 6. Now my cousin ie my aunty's daughter saying that since her mother was staying there she has total right on that built up property. 7. My father being govt servant was away from home with family since 1980. He was regularly paying all taxes for that property. 9. He is ready give what is niece's legal share, after proper distribution. But she is adamant on the point that built up property belongs 2 her only. 10. Sending notices to my father saying he has illegally occupied her property which is still in my grandmother's name. 11. ??