How should one deal with a mother who verbally and physically abuses, and prefers one of her children over the others?

An unjust mother does not lose her right over her child. Rather, he must honor her and accompany her with kindness, even if she is unjust, based on the Almighty's saying: "And accompany them in this world with kindness." And based on the saying of Ibn Abbas: "If one of them becomes angry, 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 noble Hadeeth. Among the greatest forms of honoring her is advising her, enjoining good upon her, forbidding evil from her, and being diligent in praying for her guidance.