How can injustices be redressed in the case of childhood harassment, and is it necessary to confess to the nieces and ask for their forgiveness, knowing that the questioner is now a role model in religious commitment?

Adultery is a grave and forbidden sin. Its prohibition is even more severe when committed with محارم (close relatives with whom marriage is forbidden). One who has fallen into it must repent to Allah by abandoning the sin, regretting it, and resolving never to return to it, while also maintaining the company of the righteous. One must conceal oneself and not expose oneself. The issue of restoring injustices does not apply to this sin due to the absence of coercion. The questioner is advised to strive to save their family and guide them.