What is the best way to deal with a father who conflates religion with personal beliefs, views prayer at home as proof of sincerity, interprets Hadith to suit his whims, and relies on visions for his convictions, bearing in mind that he is a حافظ للقرآن (memorizer of the Quran) and an Azhar graduate, in order to guide him to the truth without falling into filial disobedience or quarrels?

One must show respect to one's father and not raise one's voice at him, even if one is in the right. The statement that whoever goes to the mosque to pray is a pretender, a liar, and a hypocrite, is a flimsy one. The Companions considered failure to attend congregational prayer to be hypocrisy. Whoever adheres to the commands of Allah and His Messenger with a correct understanding is not an extremist. Rather, the extremist is one who innovates and declares others sinful due to permissible differences of opinion. For a person to think that he alone is saved and others are doomed is a corrupt notion. The Prophet, peace and blessings be upon him, said: "When a man says, 'The people are ruined,' he is the one who has ruined them most." Relying on dreams to abandon Sunnahs and harbor ill-will towards Muslims is impermissible, and dreams are not a source of legislation. If you see your father doing something that contradicts Islamic law, verify the ruling on the matter with a pious scholar, then choose the appropriate method to advise him gently and kindly, while still being obligated to obey him and treat him well. If he does not respond, then accompany him in kindness and beware of falling into the forbidden act he commits.