I left some money in trust with my brother and he was to return it when I needed it. But he and my mother used it all and deny that I gave them any money. What should I do?

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.

If you do not need the money that was used by your mother and your brother, then it is better for you to pardon them in order to store up its good reward for the Day when the well-doers will rejoice for their good deeds and the evil-doers will regret their evil deeds. We would like to draw your attention to the fact that the person is obliged to bear the expenses of his mother and brother when they are in need and do not have enough money to meet their needs. If they spent the money to satisfy their dire necessities such as buying food or the like, because they did not have anyone who could spend on them, they are liable to use your money since, in this situation, you are responsible to bear their expenses. This ruling is deduced from the Saying of Allah (which means): {And give the relative his right, and [also] the poor and the traveler, and do not spend wastefully.} [Quran 17:26]; and also, from the Hadeeth that a person went to the Prophet and said: “O Apostle of Allah! To whom should I show kindness? He replied: “Your mother, your sister, your brother and the slave whom you set free and who is your relative, a due binding (on you), and a tie of relationship which should be joined." [Abu Daawood]

If they used your money without having a dire need while someone else could spend for them and you are in need of that money, then you have the right to demand the money. If they deny taking your money, then they have to confirm their claim by swearing by Allah and you have to present sound evidence to prove your claim to the authorities.

Allah knows best.