What is the ruling of Islam regarding brothers killing their corrupt brother with poison after he exhausted the family and caused the death of their father? Is there an expiation for that? And what if this young man is still alive?

Whoever intentionally and knowingly curses Allah has committed disbelief and exited the fold of Islam, whether he was joking or serious, angry or pleased. This is based on the Almighty's saying: "Say, 'Is it Allah and His verses and His Messenger that you were mocking?' Make no excuse; you have disbelieved after your belief." Scholars have unanimously agreed on the disbelief of anyone who curses Allah or His Messenger, or who mocks Allah, or His verses, or His messengers, or His books; such a person is a disbeliever. The punishment for an apostate is execution after he has been asked to repent, and this حد (prescribed punishment) is applied only by the ruler, not by individuals. Parents must raise their children upon monotheism and instill the love of Allah and His Messenger in their hearts, protecting them from deviations. If the young man was under the influence of drugs at the time of cursing, many scholars are of the opinion that the apostasy of an intoxicated person is not valid.