What is the ruling of the Sharia regarding dealing with the husband’s mother who expels her son’s wife and harms her and her children, and her youngest son incites her to do so, especially since she caused the imprisonment of her eldest son and her grandson, and her other youngest son prevents others from visiting her?

The husband must be dutiful to his mother by visiting her, calling her, or by seeking mediation from someone who can influence her, all while supplicating and frequently seeking Allah's help. His defense of himself in court is good, and he may file a lawsuit against his brother or be patient with him. Also, the attempt to move the husband's mother from his oppressive brother's home is a good idea. It is permissible for you to refrain from visiting your mother-in-law currently to prevent harm, especially since visiting her is not obligatory for you.