What is the ruling on my brother taking an interest-based loan from a bank, given that real estate rental prices are extremely high in his country (Chad), and it is impossible to own a house except through loans, bribery, or stealing state funds, and that the Ministry of Finance itself deals with usury?

Borrowing with usury is unanimously prohibited unless there is a necessity deemed legitimate by Islamic law, such as obtaining housing. For it to be permissible, it is stipulated that a person cannot find owned housing or rented housing (if they cannot rent without hardship), that they cannot find someone to lend them a goodly loan, and that they build housing only to the extent of their need. As for your brother's work in a ministry that deals with usury, if his work does not involve assisting in forbidden acts, then it is permissible. Otherwise, it is not permissible except out of necessity.