Though this property belonged to your grandfather, upon your grandfather's intestate death (if your grandfather is not living now), his self acquired properties shall automatically devolve equally upon his legal heirs consisting his wife and children and his mother (if alive). Now presuming that your grandparents are not alive, then his properties shall be equally divided into 5 shares and your father is entitled to one such share.Upon your father's intestate death, his own legal heirs i.e., his wife (your mother) and 5 children shall inherit 1/6th share in his share of the property equally. Therefore you are entitled to 1/6th share of 1/5th share of the property that was left behind by your grandfather.
You can enter into amicable talks and settlement with the co-sharers, if nobody is ready for an amicable settlement then you can file a partition suit seeking partition and separate possession of your entitled share in the property.