The property that belonged to your grandfather, upon his intestate death, devolved equally among all his legal heirs.
If it is presumed that your father was the only legal heir to your grandfather, then the entire properties automatically devolved on your father (though the revenue records are still in the name of yor grandfather).
Thus, upon your father's intestate death, this property or his share of property shall again devolve equally on all his own legal heirs consisting his wife and children (and also his mother if she is living or survived his death);
Now, as you said that you are 4 sisters and 2 brothers, with your mother, this property shall be divided into seven equal shares and you are entitled to one such share.
If others do not agree for partition or any amicable solution/settlement, then you may file a partition suit seeking partition and separate possession of your rightful share with metes and bounds.
This is the position of law, if you want to know more about it you may go through the Hindu succession Act for more clear picture on the subject.