If man has wife designated as DPOA for himself and she for him and both have revoked their rights, how do we proceed?

Mother and father are not able to make financial decisions and have given the right to their son. They have turned over all trust rights to him, documented it and is notarized. For financial "stuff" not in trust, they have durable power of attorney assigned to each other with son as the alternate if they can't or revoke their rights. Is the document that states the above for the Durable POA all we need to go to the financial institutions in order to help manage their money or do we need to have a signed document stating they give up their rights in their durable power of attorney document?