What is the ruling of Islamic law concerning dealing with a disobedient son who curses his mother and threatens her with death, treats his brother with violence, demands his father's money, refuses psychological treatment, and whose mother fears handing him over to the authorities or disinheriting him?

Disobeying parents, insulting them, and assaulting a sibling are major sins. A son has no right to demand money from his father if he is an adult and capable of earning a living. It is not permissible to disinherit a disobedient son, as inheritance is a right apportioned by God, and it can only be withheld if there is a legitimate Sharia (definition) impediment. It is recommended to have the son treated by a Muslim psychiatrist, as there might be underlying medical reasons. The parents should also review their relationship with God, renew their repentance, and frequently supplicate for their son's guidance.