Is a father obligated to treat his marriage-aged sons justly, those whom he refuses to spend on, if he spent a large sum (around 150,000 EGP) on his daughter's marriage? And if he is obligated to do so, should he give them the same amount or double it?

A father must marry off his children if they need to marry and do not possess the means. This is part of the obligatory maintenance (nafaqah (definition)), and it does not require equal treatment between males and females; rather, each child is given what they need. If a father marries off his daughters but leaves his sons unmarried despite their need and his ability to marry them off, he incurs sin. If a father spends excessively on his daughter's marriage beyond what is needed, the excess is considered a gift and requires justice among the children, such that a male receives double the share of a female.