1)was it your grand father self acquired property? did he leave any will or he died intestate ? if he had self acquired property and he died intestate on his death his 3 sons would have 1/3rd share in property . (I presume that your father dosent have any sisters).
2) your father should make an application of mutation of property in his name and that of his brothers .enclose copy of death certificate of his father .
3)since your cousins are not permitting your father to sell his share your father can file suit for partition of property . subsequently your father can sell his share .
4) your father can prepare a will bequeathing his 1/3rd share to his 2 daughters . as far as construction on third floor is concerned you cannot carry out any construction without consent of municipal corporation and of all your cousins
