What is the ruling on the husband's family taking his money without his knowledge, giving it to his brother, and then denying it?

It is not permissible to judge a specific situation based solely on hearing from one party. However, generally speaking, trusts must be safeguarded and returned to their owner upon request. Disposing of them without the owner's permission is a forbidden betrayal. Allah Almighty says: "Indeed, Allah commands you to render trusts to whom they are due" and "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]." Likewise, it is not permissible to take anyone's money except with their permission, for the Muslim's wealth is inviolable except with his willing consent. "Every Muslim's [things] are sacred to another Muslim: his blood, his wealth, and his honor." And whoever takes a Muslim's money unjustly will meet Allah, and He will be angry with him.

Even a father, who has a special right to dispose of his son's money—"You and your wealth belong to your father"—his disposal is limited to his needs and, according to the majority of scholars, must not exceed them. Those who permit it, such as the Hanbalis, stipulate that he must not harm or wrong his son, nor take anything that his son needs, nor give from his son's money to another except with the willing consent of the owner of the money. Abu Hanifa, Malik, and Ash-Shafi'i, on the other hand, hold that a father may only take from his son's money to the extent of his need.