What is the ruling on a father's financial support for university and marriage expenses, and is the eldest brother obligated to return the large sums of money he took from his father, which led to the deterioration of the father's financial situation and affected the rest of the siblings?

The father is not obligated to financially support his children if they are self-sufficient through wealth or capable of earning. University tuition fees are not considered part of the obligatory financial support. Some scholars hold the view that a father is obligated to help his children marry if they need to and he is financially capable. The preponderant view, in our opinion, is the obligation of equality among children in giving gifts. Therefore, if a father favors one of his children by spending on them without the consent of the others, he is sinful and must repent and ensure equality among them. The eldest son is not required to return what his father spent on him; rather, the father must give the remaining children an amount equivalent to what he spent on their eldest brother, unless they consent to it otherwise.