How should a dutiful son behave toward his parents given the actions of his father, who pays off the debts of his divorced daughter, who is accustomed to borrowing and spending irresponsibly, yet withholds money from his son under the pretext that he does not need it, and seeks to sell his apartment during his lifetime to bequeath the money solely to his eldest daughter, especially since the son believes that the father's actions encourage the sister to extort, and that this psychologically affects the son and his family and professional life?

It was part of Allah’s wisdom that people are a trial for one another. There is no cure for trials more beneficial than patience. Allah’s pleasure is contingent upon the parents’ pleasure. Preferring some children over others is not permissible, unless it is a reward for a gift or for the reformation of one of the children. As for what the father did by selling his apartment to his eldest daughter alone, it is haram, because it is a preference and a deprivation of the son's right. However, the father's injustice does not justify the son reciprocating the mistreatment. Rather, he must be patient and dutiful towards his parents, advising them with wisdom and gentleness. If they do not respond, then let him entrust his affair to his Lord and remain dutiful to them. For Allah Almighty said: "But if they endeavor to make you associate with Me that of which you have no knowledge, do not obey them, but accompany them in [this] world with appropriate kindness."