Does showing kindness to those who have been backbitten and wronged atone for the sins of backbiting and wrongdoing, and what is the advice regarding this?

If you are able to seek forgiveness from those whom you have backbitten without incurring their resentment, then do so. Otherwise, seek general forgiveness from them by saying to one of them: "Forgive me if I have wronged you in any way, and I also forgive you." If that is not possible, then frequently seek forgiveness for them and speak well of them in gatherings, hoping that this will benefit you with Allah on the Day of Resurrection. It has been reported from some scholars that seeking forgiveness for the one who was backbitten is sufficient, without needing to directly seek their forgiveness.