I am a recent convert who is under Taqiyya from my family, and for diwali, a festival, my family bows towards idols and makes prayers. Is it permissible for me to bow in front of idols with no intention of believing in idols or polytheism so that my family is not suspicious of me? Is it enough that I in my heart I know that the only God is Allah SWT and he has no partners?

Not bow to idols. Bowing is a sign of worship. You have to not do that.