Does divorce take effect if the wife spends the night at her family's house for any reason whatsoever, knowing that the husband swore an oath of divorce that she would not spend the night there after visiting them? And if it does take effect, what is the expiation for it?

If someone swears by divorcing his wife that she will not spend the night at her family's house, then if she spends the night there willingly, the divorce takes place. However, if the overnight stay was due to an irresistible force, then the intention of the one who swore is considered: if he had an intention, it is acted upon, and if he had no intention, then the reason for the oath is considered. So, if the reason was her disobedience, she is not divorced because her overnight stay was not an act of disobedience. But if the reason for the oath was the husband's circumstances and his need for his wife's service, then she is divorced.