How can one make a father understand the حرمة (prohibition) of lying and backbiting without angering him or being accused of disobedience, especially given that the father is elderly and frequently lies and backbites?

Allah has warned against lying and backbiting, and the prohibition of both is mentioned in the Quran and Sunnah. What was mentioned about the father—lying, backbiting, distance from the remembrance of Allah, harshness, and frequent problems—are serious matters. It is advised for the questioner to supplicate extensively for his uprightness and righteousness, and then to seek the mediation of people of virtue to counsel and admonish him. She should not be ashamed to advise him or fear his anger, while preserving all his paternal rights.