Is one who wishes for the death of his grandmother, who harms his mother and wife with her tongue, sinful, and how should he deal with her?

It is not permissible to abuse or speak harshly to one's grandmother, for she has a right to dutifulness just like one's mother, even if she is abusive. If she acts abusively, one can enjoin her to good and forbid her from evil gently and courteously, without harshness. Being dutiful to one's grandmother is a great opportunity to gain Allah's pleasure and earn reward.