Is it permissible for a Muslim to pray according to the Noble Prophetic Sunnah secretly from his Shiite family, and is it permissible to perform ghusl (ritual bathing) like the Shiites?

The Sunnah is Noah's Ark: whoever boards it is saved, and whoever lags behind drowns. Advise your family with wisdom and good counsel, and supplicate for their guidance. If you fear harm to yourself from openly declaring your belief, then it is permissible for you to conceal it, as in the story of the believer from Pharaoh's family and the believers in Makkah who concealed their faith. The Prophet, peace and blessings be upon him, also ordered Abu Dharr to conceal his Islam at the beginning. Concealing faith does not mean committing falsehood openly, except for one who is coerced. And if you are unable to pray with the Ahl al-Sunnah wal-Jama'ah, then pray alone; it is better than praying behind innovators.