What is the ruling on sitting with family members who engage in backbiting? Is it sufficient to leave the place and return to it later, or is it obligatory to completely abandon the gathering?

It is impermissible to sit with people who are committing sins while they are engaged in their sin, for Allah the Almighty says: "And He has already sent down to you in the Book that when you hear the verses of Allah disbelieved in and ridiculed, then do not sit with them until they enter into another conversation. Indeed, if you did, you would then be like them." So, if you are unable to condemn the evil, then leaving the gathering is the correct action. Do not return to it until the evil is removed. There is no harm in returning once the evil has ceased, for Allah the Almighty did not absolutely forbid sitting with them.