How does a father divide the gift of his properties among his children (two sons and a daughter), and is it obligatory to apply the rule "to the male, what is equal to the portion of two females"? If so, can the males voluntarily relinquish a portion of their share to their sister, and how should the gift contract be drafted in this case?

Justice between children in gifts and endowments is obligatory and is achieved by giving the male the same as the female. If the children agree that one of them should relinquish their share to another, there is no harm in that, provided that the one relinquishing is an adult of sound mind. This is not valid from a minor or a prodigal. A gift is effected by offer, acceptance, and mutual consent, and everything that is customarily considered a gift. As for the legal formula, one should refer to specialists.