Normally, the asset allocation is between spouses. Please provide additional information about the property received, basic description, when/how your parents acquired the property, any information as to how the transfer took place at the time of divorce, etc.
There are at least two possible answers based on the information provided.
1. Your father retained a life estate in the property and you and your sisters were gifted a residuary interest in the property that took effect upon his death. In this case, your basis in the property would be its fair market value on his date of death. Upon sale you would subtract from the selling price this basis, any improvements you made after his death and any closing costs related to the sale (commission, title insurance, transfer tax, etc). This amount would be the gain to be reported and allocated between you and your sisters.
2. You and your sisters each obtained as a gift, an undivided 1/(#of siblings + 1) interest in the property. Your basis would be your percentage interest of your grandparent's basis in the property plus any improvements made since they purchased it. Upon your father's death you would each be allocated a percentage of your father's interest. This portion of the basis would be at fair market value on his date of death.
If possible you should consult with the attorney that handled the original transfer to assist you in determining your basis for gain or loss.