Is it permissible to dispose of the money held in trust (which is usurious interest-bearing loan money) to repair the roof of the house of the one entrusting it to him, who lives far from his wife and does not want to give her money for the repair?

You are not permitted to dispose of the money your brother-in-law deposited with you without his permission, as you are entrusted with it. If the dwelling is unfit, your sister has the right to demand her husband repair it or provide another. If he refuses, she may take the matter to court.