Is repeated complaining to family and friends about the treatment of the husband's family and the husband considered forbidden backbiting? And is continuing a marriage despite repeated abuse from the husband considered patience for which a person is rewarded? And how can one atone for the sin committed?

If the complaint involves mentioning people's faults and shortcomings, it is backbiting (gheeba) and forbidden, unless it is directed to someone who is expected to redress an injustice, or its purpose is to seek advice and guidance, given the valid legal benefit therein. As for insult and abuse, they are never permissible. Allah has commanded kind treatment of one's wife. Allah has promised a great reward to those who are patient. Complaining without backbiting does not invalidate one's deeds or contradict patience, though patience is more virtuous. The best way to endure harm is to fear Allah, seek His help, maintain remembrance (adhkar), and treat the wrongdoer with what is best. The wife should endear herself to her husband to win him over. The expiation for backbiting is repentance to Allah, seeking forgiveness from those one has backbitten, or seeking forgiveness for them and mentioning them positively if one fears increasing the harm.