I am so sorry for your loss.  It is unclear to me here if you and your brother have already been appointed as co-executors of the estate, because you can not act unless and until the court has appointed you. You will need not only her death certificate but Letters Testamentary. Now, once appointed, generally speaking you can act individually but I would check with the bank to make sure. And if it may be too difficult for your brother to travel and act in his capacity, he may want to consider renouncing his appointment.  You can act alone.  Good luck.