What is the ruling regarding a father's will that deprives daughters of their share in some lands, giving them instead lands of lesser value? Is it permissible to sell the share of one of the female heirs in common (undivided) prior to the distribution of the inheritance? Furthermore, is it Islamically permissible for this daughter to side with her brothers against her sister, who is demanding her legitimate right to the inheritance?

First, it must be noted that selling your share of the inheritance in an undivided state is impermissible, as it constitutes the sale of an unknown entity.

As for your question, it is not permissible for you to side with your brothers in their dispute against the sister who is demanding her legitimate right to all the lands. Your brothers are unjust if they prevent her from receiving her share, for every heir has their legitimate right to every plot of land.

Giving some heirs their share from lands of lesser value is an act of injustice and transgression. Your father's will, which stipulates that the better lands be given to the sons without the daughters, is invalid because it is an unjust will and one made to an heir. A will made to an heir is forbidden by Islamic law, based on the Prophet's (peace be upon him) saying: "Indeed, Allah has given every rightful person his right, so there is no will for an heir."

The Islamic division of lands is done by determining the share of each heir in every land, and then you can divide it among yourselves on that basis.