Is it permissible for my brother to take out a loan from the bank to purchase a car for disabled individuals, provided that the installments are paid from his disability pension?

As for the loan, if what is meant by it is a legitimate financing transaction such as "Murabaha" with an Islamic bank, then there is no harm in it. However, if the transaction is with a usurious bank by borrowing the price of the car and then repaying it with usurious interest, then it is not permissible except out of necessity.