If you lose mental capacity, then there can be no one with the permanent authority to manage your financial affairs, without an Enduring Powers Of Attorney. Then, to appoint someone to your family or advisers, you have to apply to the respective authority in your state or region.
You can control the powers given to the attorney by placing limits or conditions in the Enduring Powers Of Attorney. For example, you can authorize the attorney to pay the bill, but not to sell the property.
If you need any guidance for Enduring Powers Of Attorney, you can contact Jackson and Associates in South Australia.