How can my father be cured of the infidel jinn that afflicted him through sorcery, leading to the deterioration of his memory, despite some scholars saying that his recovery is impossible after such a long period, and my belief that the Holy Quran contains healing?

The statement "Your father's recovery is impossible" is incorrect, for healing is in the hands of Allah. The Messenger of Allah, peace and blessings be upon him, said: "Allah has not sent down a disease except that He has sent down a cure for it." The greatest cure for magic and jinn is ruqyah according to the Shariah. You can benefit from the previous fatwas (31174, 32150, 4524). We advise you to take your father to a shaykh known for his adherence to the Sunnah to perform ruqyah according to the Shariah, while being cautious not to go to magicians and charlatans.