Is a father considered unjust if he refrains from giving money to his son to buy a computer and other things, while his brothers do so?

A father is obligated to financially support his children who are not yet adults or are unable to earn a living. This includes providing food, drink, clothing, and housing according to what is customary. Beyond these basic needs, financial support is not obligatory. If the father provides what is obligatory, he is not considered unjust if he does not meet all of his children's demands.