In a Mudarabah operation that took place between him and his brother, and it became clear that it was a fraud, does the claimant guarantee half of the total money or only the money he collected from people?

If the money is given to the mudarib (investing partner) with the permission of the capital owners, then the one who gave it is not liable. The capital owners can hold the aggressive mudarib accountable. However, if the money is given without the permission of the capital owners, then the one who gave it is liable for it. Silence is not considered permission unless there are supporting indications. In this case, each person is liable for the money they collected due to their negligence. If they both participated in collecting the money, then both are liable for all of it.