Is it considered haram for the wife to visit her grandmother in the same building if the husband had forbidden her from going out without his knowledge, then permitted her to visit her grandmother during an argument, then said that his prohibition was a threat, and she does not inform him of her visits to avoid problems?

A wife's visit to her grandmother without her husband's permission makes her fall into sin. And since the husband conditioned the prohibition of his wife on her going anywhere without his knowledge, the oath has been broken by her going to her grandmother without his knowledge, and his retraction is not valid according to the majority of scholars. If the husband intended by his oath merely a threat, then an expiation for breaking an oath (kaffarat yameen) is obligatory upon him. The husband must be informed that the oath has been broken. Understanding and respect should prevail in married life, and they should avoid problems, and the husband should not use words of divorce or prohibition.