Is it permissible for the sister to demand her share of the apartment that the deceased father registered to his son with a fictitious contract? And should the valuation be on the day of death or on the day of distribution? And is this considered a valid gift or a void contract? And does the son's possession of the apartment suffice in place of the father's verbal acceptance?

A simulated sale (بيع صوري) is treated like a gift (هبة). For a gift to be valid, it is not a condition to utter a specific formula; rather, it suffices to have what customarily indicates it. Scholars have differed on the obligation of fairness (عدل) between children in a gift, with the preponderant opinion being that it is obligatory. Most scholars hold that if the donee (الموهوب له) has taken possession of the gifted item, their right to it is established upon the death of the giver (الواهب), whether the gift was fair or not. However, some scholars are of the opinion that the gifted item must be returned, even after the giver's death. From a judicial perspective, if the ruling that mandates restitution is the one adopted by the judiciary, then the prohibited favoritism (تفضيل ممنوع) in the gift must be proven. Maintenance (نفقة) differs from a gift, as equality between children in maintenance is not obligatory; it is determined by need.