Is it permissible to obey one's parents in a sin that does not reach the level of disbelief, if one fears for their religion from temptation should they disobey them, knowing that they command them to do forbidden things and may tempt them away from their religion? And does the ruling change if one is not certain about their tempting them?

The fundamental principle is that a Muslim's outward actions and inner beliefs should be consistent. It is not permissible for him to go along with people of falsehood in word or deed, as this is the blameworthy compromise (mudahanah), as stated in His Almighty's saying: "They wish that you would compromise, so they would compromise" (Qur’an 68:9). It is not permissible for a Muslim to go along with falsehood out of desire for worldly gain or imagining harm. Allah has condemned those who reside in lands of disbelief while being able to emigrate, as in His saying: "Was not the earth of Allah spacious enough for you to emigrate therein?" (Qur’an 4:97).

If a Muslim is compelled to remain in a false environment and fears severe harm if he does not show deference, then it is permissible for him to do so to the extent of the necessity. However, this does not apply to mere pressures, or requests to attend evil gatherings, or similar situations. Rather, he must fear Allah, be patient, and seek knowledge from trustworthy sources. If the matter necessitates departure, then he should do so. And whoever fears Allah - He will make for him a way out. And whoever seeks Allah's pleasure by incurring people's displeasure, Allah will be pleased with him and make people pleased with him.