Transfer the money to my brother's account. Sister-in-law doesn't pay back the money.

Transfer the money to my brother's account, and if you don't return it, it's unjust enrichment. According to relevant information: the other party does not pay back the money transferred to another person's card: the other party does not pay back the money, which can be solved through judicial channels. If the money received is not returned, it belongs to unjust enrichment and should be returned. If you still refuse to return it when asked, you may be suspected of embezzlement.