Most unlikely that a bank would take it on itself to divide up money amongst next of kin. They may just have released money for funeral expenses etc subject to some indemnities. If the bank itself divided the assets it could end up being deemed to be executor de son tort - i.e. by default for dealing ( "intermeddling" is the term used ) in the estate without the formal authority of a grant of probate or letters of administration..
No matter how friendly you are with other members of the family it is unusual to be asked to sign a blank page, and rather naive and foolhardy to sign a blank sheet of paper under any circumstances. Perhaps you are winding us up?
If this is a genuine problen, go to a solicitor