Praise be to Allah, the Lord of the Worlds, nd blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. If your wife enters the house of her sister in the presence of her husband, then she will be divorced thrice. If you intend to stop her from being in his house, while he is there in, she will be divorced in this condition also. If you intended to prevent her to enter her sister’s house only while her husband is in house, in this condition, if she was in her house and her husband entered afterward, then she would not be divorced, because the oath is always on the intention of the swearer. Allah knows best.