Must the husband urge his wife to visit her mother, even though he knows of the mother's desire to ruin their marital life?

You are not obliged to allow your wife to visit her mother; rather, you have the right to prevent her from doing so if the situation is as you described, as this is better for preserving your family and preventing your wife from being corrupted against you. A husband has the right to prevent his wife from going out, even for the illness or death of her parents.