How should I act towards my family members who constantly backbite people? Should I abandon them and not sit with them, given my mother's need for my help? And what should I tell them if they ask me why I don't sit with them? Is it permissible to lie in this situation for fear of showing off?

Your duty is to strive, to the best of your ability, to prevent your family from backbiting Muslims, using a gentle approach and praying for their guidance. Warn them about backbiting by citing texts that prohibit it, such as the Almighty's saying: "And do not backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah; indeed, Allah is Accepting of repentance and Merciful." Try to divert them from forbidden speech and engage them with entertaining conversations, like stories of the prophets and righteous predecessors. If your efforts are unsuccessful, then you must avoid sitting with them and turn away from them so that you do not hear their words, while staying close to your mother when she needs you. If they ask you about the reason for your distance, there is no harm in stating the truth, and this is not considered hypocrisy. Be diligent in truthfulness while avoiding sitting with them during backbiting.