Son's and daughter's right on fathers property

I am my father's only daughter and unmarried. I have 3 brothers who are all elder to me and are married. My father is retired from the railways and has a 2 storeyed house in our hometown. My mother is a homemaker. My eldest brother and the youngest one are unemployed and are being taken care of by parents. My 2nd brother is employed in railways and I am a private employee. My 2nd brother and I have taken care of family requirements to some extent not all.We have all been relying on dad's pension and house rents. Now its time for property settlement as my dad is already 72 and is sick on bed and my second brother is threatening and claiming his portion, in fact wants more as he thinks he has done a lot for the family and has never relied on Dad since the time he started living separately with his family. He is threatening that he will file a complaint against mom n dad and claim all that he can. Now my question is, How much rights does each son have on the property and being an unmarried daughter how much do I have? What can I do to save my parents from this threatening?