How should the relationship be with the wife and the brother after discovering his frequent visits to the home during the husband's absence and his being alone with his wife, knowing that the husband is aware of the danger of a man being alone with a non-mahram woman, and taking into account that the wife and the brother have sworn that nothing happened between them beyond conversation?

The husband must prevent his brother from entering upon his wife in his absence, and prevent his wife from permitting any non-mahram to enter his house or to be secluded with him, or to display her adornment before him, or to speak with him in a suspicious manner.

The noble Hadith confirms the husband's right that his wife should not permit anyone into his house except with his permission, and warns against the husband's relatives (al-hamu) entering upon women because "al-hamu is death."

If the wife is upright, then keep her with kindness and fulfill your right of guardianship over her, and help her obey Allah. However, if she does not obey you or if suspicion arises from her, then it is recommended to divorce her, or it may even be obligatory.