Making an oath of divorce not to return his sister to her first husband but agreeing to it later
Q: A woman got divorced from her husband and her brother gave her in marriage to another man. When the woman fell ill, she went to stay at her brother's house until her condition improved. However, when her second husband came to take her home, she refused claiming that the treatment was not yet completed and that the doctor prevented her from having sexual relations with her husband. Her husband suspected that her brother wanted her to be divorced in order to return to her first husband.
The brother took three, ten, and a hundred oaths of divorce to assure the second husband that he did not even think about returning her to her first husband. The brother says he was truthful when he took that oath. Later, the second husband divorced the woman and everyone thought it would be better for her to return to her first husband, while the brother had no intention of this from the beginning.
If the woman returns to her first husband, does her brother's oath of divorce become effective? Please enlighten us.
If the reality is as you mentioned, that when the brother took the oath of divorce, he had no intention of returning his sister to her first husband, (Part No. 20; Page No. 110) and that the idea of returning her to him came after she was divorced from her second husband, the brother will not be breaking his oath by returning her to her first husband. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.