Does a divorce take place if a husband tells his wife, "If you ever ride again with any non-mahram person in the front seat, then you are divorced," and then she rides with her daughter's husband's brother, not alone but with her sisters?

The wife should be aware that her seclusion with a foreign man inside a car is a sin, and it is considered unlawful seclusion (khalwa). Regarding the condition of divorce upon the wife riding with a foreign man, the oath is based on the intention of the one who swears it. If the husband intended that they should not be alone together, then there is no breach of the oath if others were present with them. If he had no intention at the time of swearing the oath, and the reason for the oath was the sin of seclusion, then he also does not breach the oath if there was no seclusion. However, if there was no intention or purpose, or if he intended her riding with a foreign man under any circumstances, then the divorce is effective according to the majority of scholars. A kaffarah (expiation) for breaking an oath is required according to Ibn Taymiyyah if he did not intend divorce. In the event of a divorce occurring, she can be taken back (revoked) before the end of her waiting period (iddah) if this divorce does not complete the three divorces.