Grandchildren's right on grandfather's property

Hi, my grandfather has self acquired property. He is not alive now and has not made any WILL before his death. He has four daughters (A, B, C and D) and three sons (X, Y and Z). My grandmother is still alive but her mental condition is not good (She is around 90 yeras old). The second son of my grandfather, Y and his (Y's) wife dead 10 years back. But the couple (Y and his wife) has a son (27 yrs old) and a daughter. I am the son of my grandfather's eldest son X. My age is 26 yrs. My father X is alive. My uncle (My grandfather's youngest son Z) is planning to sell the property. It is clear that all the children of my grandfather has to sign the documents. I have many important questions: 1. I wanted to know whether my signature is compulsory for selling the property? 2. If my father doesn't like to sell the property, can rest of my grandfather's children sell their share of property? 3. If my father has signed the documents without taking the money, can he go to court? Please help me by giving correct answers.