What is the ideal solution for dealing with a father and a brother who revile the religion and the Messenger, may Allah bless him and grant him peace, and will the questioner be held accountable if he does not advise his father due to his quick temper?

Cursing the religion is an act of disbelief and apostasy. The matter becomes more severe by cursing the Messenger and slandering the Sharia. It is advised to be patient and wise, and to persistently invite the father and brother to guidance with kindness, explaining the seriousness of their actions. Seek help from reformers and pray for their guidance. If the duty of enjoining good and forbidding evil is fulfilled, the questioner will not incur sin. However, if such denunciation increases their transgression, it is better to desist. The father's right to companionship with kindness is not nullified by disbelief, as stated in the noble verse: {But if they endeavor to make you associate with Me that of which you have no knowledge, do not obey them, but accompany them in [this] world with appropriate kindness}.