What should I do regarding my family's lack of interest in prayer and their committing of sins, after my numerous attempts to invite and guide them?

May Allah reward you for your eagerness to guide your family. Filial piety entails inviting one's parents to Allah the Almighty and gently, not harshly, enjoining them to pray and perform other acts of worship. If you cannot invite them directly, then let it be through someone who has the ability to influence them. You must be patient and persistent in inviting them, and do not despair of their guidance. Even if they do not respond, their shortcomings will not harm you. Increase your supplications for them in their absence.