Is it considered unjust and humiliating to the wife for the husband to threaten her with divorce to appease his mother, knowing that she has not neglected his marital rights, and he wants her to live with his mother permanently despite her discomfort?

You should know that the right of the mother is great and takes precedence over the right of the wife, but this does not mean injustice to the wife. Rather, the husband must fulfill the rights of both his mother and his wife completely, and prioritize his mother's rights in case of a conflict. The husband has the right to reject his wife's request for a separate dwelling and to choose divorce to please his mother. It is advised to be patient with the husband's mother and help him honor her, as there is a great reward in this, and indeed, whoever does good will be rewarded with good.