There is no definitive answer to your query. It depends on several factors: Is your father alive? How did he give the money? Was it a joint account? Did he approve the transaction, or was it done without his approval? What evidence do you have, etc.?
You will need to consult with a lawyer to determine how strong a case you have against your brother, if at all. In any case, a legal action would need to be filed under civil law unless you can demonstrate a criminal breach of trust or direct fraud. The case could take years, so I don't have much hope for your mother receiving immediate relief.
In any case, if you provide all the details of the circumstances, a lawyer will be able to advise you on your position. Remember to consider the lawyer's fees and other costs in relation to what you might recover.