How can one overcome the soul that incites to evil (an-nafs al-ammarah bi's-su'u), and what is the practical solution for someone who has committed a grave sin and wishes to remain steadfast? And how can one deal with parental injustice and their ill-will without disobedience or accepting the injustice?

Overcoming the self that incites to evil is achieved by striving against it. Insisting on sins is caused by heedlessness and desire, and each has a cure. Being dutiful to one's parents is a cause for Allah Almighty's pleasure and happiness in this world and the Hereafter. Even if they wrong you, it is not permissible for you to cease being dutiful to them. You can clarify the truth without stopping your good treatment of them, just as our master Abraham (peace be upon him) did with his father. So, you must fear Allah, mend what is between you and your Lord, and be dutiful to your parents.