What is the ruling on the money the questioner received from a car that the Amir gifted to his father, given that the father singled out three of his sons with cars, to the exclusion of the others?

A father is Islamically required to be just among his children in giving gifts. This is considered obligatory by some scholars. If the cars were a gift from the Amir to your father, and then the father gifted them to some of his children, this falls under the ruling of justice, and it is not permissible for the father to favor some over others. However, if the Amir gifted them directly to the children, there is no issue with its validity. It is disliked for a father to seek gifts for some of his children and not others if there is no reason, and it is recommended to treat them equally even in matters of affection, such as a kiss.