What is the Sharia ruling on an oath of divorce uttered by the maternal aunt's husband, forbidding her from entering the questioner's house, knowing that the aunt was unaware of the oath and entered with the intention of maintaining kinship ties and reconciliation?

If the wife has entered her sister's house, then if the husband intended to effect a divorce, the wife is divorced. But if he intended to prevent her from entering and did not intend divorce, then an expiation for breaking an oath is incumbent upon him. The wife's knowledge of the divorce being conditional is not a requirement.