Does a wife's divorce occur after her husband swears an oath of triple divorce that she will not go to her brother's wedding, and then she goes against his will after her parents arrive?

The majority of scholars hold that a conditional divorce takes effect upon the fulfillment of the condition, and this is the preferred view. So, if you swore by triple divorce that your wife would not attend her brother's wedding, and she attended in the manner you intended, then according to the majority, the triple divorce takes effect. Consequently, she becomes unlawful for you until she marries another husband in a valid marriage and he divorces her after consummation. Some opinions suggest that you would owe an expiation for an oath (kaffarat yamin) if you did not intend divorce. However, if you did intend divorce, then a single divorce takes effect, and you may take her back before the completion of her waiting period (iddah) if this divorce does not complete the three divorces.