Is it obligatory to sit with relatives who corrupt one's religion with ignorance and doubts, especially if one's mother insists on it, and should religious discussions be held with them that might harm relationships?

If you are not qualified to debate those who spread misconceptions, then avoid arguing with them so that you are not affected by their misconceptions. Strive to seek knowledge to be strong enough to refute them. It is not permissible for you to sit with them while they are engaged in falsehood without denouncing it, in accordance with His, the Almighty's, saying: "And He has already revealed to you in the Book that when you hear the verses of Allah being denied and ridiculed, do not sit with them until they engage in another conversation. Indeed, in that case, you would be like them." And if you are unable to denounce them or silence them, then you must leave the gathering, and that is not considered disobedience to your mother, because there is no obedience to a creature in disobedience to the Creator.