There is not definitive answer to your query.
It depends, is your father alive ? How did he give the money, whether it was a joint account, did he approve or was it without approval, what evidence do you have etc.
You will have to sit with a lawyer and figure out how strong a ground you have against your brother, if at all. In any case, a case filed will have be to under civil law, unless you are able to show criminal breach of trust or a direct fraud. The case will go on for years, so i don't have much hope for your mother for immediate relief.
In any case, if you give all details of the circumstances, a lawyer will be able to tell you where you stand. Remember, to work out how much lawyers fees and other costs will be in the case against what you can recover.