How should I deal with my sister, whose immorality I suspect, and what should I do if I confirm it, knowing that I am a Muslim who is not religiously committed and that my father is not concerned for personal reasons?

Parents are obligated to protect and care for their daughters by teaching them the Sharia (definition), raising them with good morals, keeping them away from vice, and preventing them from attending bad gatherings and associating with foreign men. It is advisable to implement an educational program for daughters and monitor them without accusation, and to strengthen their faith by encouraging them to do good and warning them against evil through the texts of the two revelations (Quran and Sunnah (definition)). The guardian must also be a good role model and first rectify himself.