You'd best go to the bank and explain.Your brother , strictly, hasn't got power to act like that,even if he's named in the will as executor, until he's got probate or,not here, it was a joint account and he was one of the joint holders with your father-in-law (in which case his not being an executor would not be material as far as the bank was concerned). If he's prepared to impersonate you, you and the bank would be right to be worried! The bank shouldn't have given out statements.They'll say they were victims of misrepresentation but it doesn't say much for their security and rules of confidentiality.