How should the family deal with a disobedient son?
Question

How should a son who is disobedient towards his parents be dealt with? How should they deal with a son who threatens to kill his mother and challenges his parents, and accuses his sister of promiscuity and zina, causes scandal for his family, and always argues with guests, insulting them, reviling them and threatening them?
Praise be to Allah.Parents should give their children a good upbringing and take care of them so that they will be in a good state in both religious and worldly affairs. 
If a child grows up disobedient and rebellious, then the parents must do more and try harder to guide him and make him righteous, by reminding him and advising him, showing patience towards him, praying for him, choosing good friends for him and choosing righteous acquaintances who can visit him, and advise him and befriend him. 
His brothers, friends and neighbours should help his parents with that as much as they can. 
But if the son becomes worse and the evil and trouble he causes increases, as mentioned in the question, and admonition and discipline do not succeed with him, then it is obligatory to denounce his evil by all possible means, by threatening to hit him or actually hitting him, or seeking the help of other men in the family against him, or taking the matter to the authorities, if it is not possible to stop his evil by any of the other means mentioned. His evil should not be taken lightly or be overlooked; rather it should be stopped before it goes further and causes greater harm. 
So first of all they should follow the steps mentioned above of offering advice and guidance, reminding him of Allah, instilling hope and fear; telling him about the rights that his parents, his sister and his guests have over him; telling him that his committing this evil will make him hateful to his family and neighbours and the people around him, and they should persist with him in that, whilst being gentle and patient, and using wisdom and beautiful preaching. 
His brothers should try hard in that regard, and use wisdom and patience with him, exhorting him gently and not being harsh towards him in speech. 
But if he persists in what he is doing of severing ties with his parents and his brothers and sisters, and shunning them, then they should not speak to him or interact with him, in the hope that Allah will set him straight, and they should keep praying to Him to guide him. 
But if he does not come back to his senses and he persists in his evil ways, then they should report him to the relevant authorities and the security forces who can restrain him from doing evil and deter him from what he is doing. 
He should not be left to persist in this transgression, because of the severity of his evil and the harm that he may do to his family and the people around him. 
Over and above all that, his parents and family members should turn to Allah, for most such calamities come about because of the sins that bring evil and corruption to the household. Ibn al-Haaj (may Allah have mercy on him) said, when speaking about matters contrary to Islamic teaching that may be done by one or both spouses: 
Undoubtedly reconciling between these spouses is very rare, and even if there is harmony between them, it is not free of ills, and if they happen to have a child, he will most likely grow up disobedient and doing all manner of inappropriate things, and all of that is the result of both of them not paying attention to their duties towards Allah, may He be exalted. End quote from al-Madkhal (2/170) 
And Allah knows best.