How can one deal with a mother who abuses and slanders her children, is never satisfied with their attempts to please her, and mistreats everyone around her?

If a mother is unjust and abusive, there is no blame for the absence of affection and love towards her in one's heart, provided that this does not lead to disobeying her. For a person does not control love or hatred. It is the child's duty to honor her and treat her kindly, no matter what her condition, because the mother's right is great.