How should one deal with a mother who verbally abuses her son and reminds him of his past sins, despite his attempts to please her, especially since he witnessed her ill-treatment of his grandmother? And what pleases God in this situation?

You must repent for your ill-treatment of your mother and your shortcomings in fulfilling her rights. You must honor her, treat her kindly, and be patient with her, for her right is immense and is not forfeited by her ill-treatment or injustice. This is based on the hadith of Ibn Abbas: "Even if one of them (the parents) is angered, Allah will not be pleased with him until they are pleased with him." It was asked, "Even if they wrong him?" He replied, "Even if they wrong him." The mother's right is more emphasized than the father's, as stated in the hadith: "Your mother, then your mother, then your mother, then your father." Her shortcomings in honoring her own mother do not justify your negligence in honoring her, for she will be held accountable by her Lord for her actions, and you will be held accountable for yours. Beware of Satan's stratagems, seek Allah's help, be sincere in your repentance, and strive to honor your mother.