All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The one who is entrusted with a deposit to keep for someone else is entrusted over this deposit and whenever its owner requests it, he must return it to him immediately.
He is not entitled to lend it to anyone else without the permission of the owner of the deposit.
It was also said that if he knows that the owner of the money does not object to this, then he may lend it. However, if he doubts about his consent, it is not permissible for him to do so. This is stated by Shaykh Ibn Taymiyyah in Majmoo’ al-Fatawa.
In any case, your brother's wife is wrong by giving the deposit to her husband without your permission and she must return the money to you.
Allah knows best.