What should I do regarding my father who was committed to the faith, then returned to listening to music and singing, delays his prayers, has begun to utter words unfitting for a Muslim, despairs of God’s mercy, and exposes my young siblings to inappropriate scenes due to the television in the children’s room?

The father must repent and turn to Allah Almighty before it is too late, because the sins attributed to him may lead him to perdition in Hell. Indeed, there is fear for him of apostasy due to his uttering words that contradict the beliefs of Muslims. As for the son, he must be dutiful to his father and strive to advise him, warn him of Allah's punishment, and offer him admonitions. If that does not benefit, then he must pray for him and seek forgiveness for him, as mentioned by the author of Radd al-Muhtar.