Grandchild's legal share on maternal grandfather's ( father of mother)

I am a daughter(over 18 & married), where my mother is alive but father is not alive. I have a unmarried brother who is 18+ age. My grandfather had 2 children. My father and his sister. grandfather, father and his sister, all three is not alive. After my marriage, my mother and brother staying in a home since many years. But now my Bua's children ( children of my father's sister) has started asking their share on property by 50%. and their argument is this property(home) should be divided between my father and his sister equally. there was no will made by my grandfather or my father. Can you please let me know if their claim is valid and legal? How can I secure my mother's home?