A power of attorney, even one that is durable (i.e. remains in effect after the person is unconscious or incompetent) is no longer effective once the principal (the person who signed it) passes away. At that point in time the executor (if they have a will) or substitute trustee (if they have a trust) takes over the legal authority. Thus you should find out whether your brother has a will or a trust, and then, find out who is named as executor or trustee. That is the person who will be in charge of all financial and legal matters upon his death.