Suppose someone has a parent(or both) who, chas vshalom, became an idolater. Do their kids still have the obligation of Kibud Av Veim towards them?
The Mechaber YD 240:18 paskens like the Rambam that one is obligated to honor his father who is a Rasha. The Rema there paskens like the Tur that he is not liable. That means that Ashkenazim who follow the Rama certainly don't have to honor their father who is an idolator, and sefardim who follow the Mechaber presumably would still have to honor him. (One might claim that the Mechaber would agree to the Rema in a case of an idol worshipper, but such an assertion needs a source.)