What is the ruling of Islamic law regarding a father's discriminatory and abusive treatment of his son, refusing to allow the latter to build on the father's property despite permitting his brothers to do so, and then compelling him to pay household expenses despite his difficult financial situation and debts?

Allah has commanded kindness to parents, and spending on them when they are in need is an obligatory duty by consensus, if the son possesses more than his basic needs. If he does not possess enough, then their maintenance becomes obligatory upon his well-off siblings. Preferring one child over another in giving gifts is an injustice forbidden by Islamic law, but this injustice does not permit the son to boycott his father or fall short in his dutifulness. Rather, he should advise him gently and seek assistance from those who can advise him, striving to be kind to him to the best of his ability.