What is the ruling of Islamic law regarding the youngest son's demand for the full pension he is entitled to from his mother since her death, given the objection of the eldest son and the second wife, on the grounds that the father spent more on him than the value of the pension?

Before dividing the inheritance, it is obligatory to pay off the deceased's debts, because debt takes precedence over the heirs' rights. After the debts are settled, if the heirs are a wife and two sons, the wife receives one-eighth due to the presence of a lineal descendant, as Allah Almighty says: (But if you have a child, then for them [the wives] is one eighth of what you leave, after any bequest you [may have] made or debt.) The remainder is then divided equally between the two sons by way of ta’seeb (residuary inheritance), based on the Prophet, peace and blessings be upon him, saying: "Give the fara'id (fixed shares) to those who are entitled to them, and whatever remains is for the closest male."

Accordingly, the inheritance is to be divided into sixteen shares: two shares for the wife, and seven shares for each son.

As for the younger son's demand for the entire pension that was deposited into his father's account, he does not have the right to it as long as his father was spending on him. The principle is that a minor's maintenance should come from his own money if he has any; otherwise, it is the responsibility of whoever is legally obligated to support him. If the son believes that his father spent less on him than he was entitled to from his money, he may refer the matter to the Sharia court.