What is the responsibility and authority of the elder brother towards his sisters who commit unlawful acts, such as speaking and laughing with foreign men, especially when his parents prevent him from interfering in their upbringing on the grounds that they are still alive? And is he sinful if he raises his voice at them in anger over their silence regarding their daughters' bad deeds?

You must honor your parents and treat them kindly, and it is not permissible to mistreat them even if they mistreat you. Your father is responsible for disciplining your sisters, and you must enjoin them to good and forbid them from evil, and advise your parents gently and respectfully that your father is responsible for preventing his daughters from forbidden acts, for parents are not like others in enjoining good and forbidding evil.