What is the ruling regarding parents not reciting the Quran, their negligence in prayer, and their not memorizing verses for prayers? Is the son sinful for not advising or teaching them, and are they sinful for their lack of concern?

Parents must learn what is essential for the validity of their acts of worship. This is an obligation upon them and upon their children, out of advice and filial piety. Even if some parents do not accept this, with determination and preparing the appropriate approach, they can be taught.