Your grandmother's property, upon her intestate death shall devolve equally among all her legal heirs namely her children.
Thus the property divided among the sons alone without giving a rightful share to the daughters is an illegal act.
The daughters are entitled to their legitimate share in the property.
They can file a suit for partition and can seek for petition of all the properties by metes and bounds, with good and bad soil equally and to allot one such equal share to each of them with separate possession.
They can even obtain an order of injunction restraining your father from constructing the proposed construction of the building in the vacant plot.
The unregistered partition deed excluding the daughters and without registering the same if invalid in law, your paternal aunts an ignore the partition deed drawn among your father and his brothers and can claim their share in the property as a right.
Try to sort it out amicably instead of stretching it as a legal battle because a suit for partition before court may stretch to more than 5 years for disposal.