Yes, you can have any number, although more than 2 can become unmanageable. They can be authorised either:'Jointly' which means they must both sign any document on your behalf.'Severally' which means that any one can sign - without necessarily having the consent of the others.
If the signing of the power of attorney is witnessed by a prescribed witness (solicitor, barrister , clerk of a local court etc) and they certify they have explained it to you, the power of attorney 'endures' through any period where you loose capacity to understand what you are doing. Without that certificate, the document ceases to be valid if you can't understand your affairs. An ‘enduring’ power of attorney is the usual type.
It lasts until you either:Cancel it. This is called 'revoking' – see above.Pass away. A power of attorney ceases to have any effect after your death.
Anyone over 18 years can be your attorney. It should only be given to a person who can be completely trusted as they can do anything you can do financially such as sell or mortgage your house or operate on your bank account (unless there are limitations against this in the document). Of course, if they acted illegally by stealing your money, they could go to prison but that may not get you your money back.
No - a Power of Attorney can only be given by a person who understands what they are signing. If she has lost the ability to understand what is going on then she can not sign a Power of Attorney. Your only solution is to make an application to the Guardianship Tribunal to be appointed Financial Manager of her affairs.
It is up to the organization that you have to deal with as to what authority they require. The Land and Property Information Office which controls the ownership of real estate and therefore buying and selling of houses insist on a Registered Power of Attorney. Centrelink seems to have its own form of authority and banks usually insist on a Power of Attorney but not usually a registered one. A bank will usually have a procedure to authorize someone else to sign on an account and this may solve the problem of paying bills.
The Guardianship Tribunal has Power to grant the right to manage someone's affairs to another or to a government body named The Protective Commissioner. The person or body appointed is called a Financial Manager. If someone is physically or mentally unable to care for themselves, an application can be made to the Tribunal for a management order. The Tribunal will look at evidence as to the person = s condition from their doctor and others. If the Tribunal is satisfied of the person’s inability to manager themselves, it will make the order. If a private individual is appointed, the Tribunal will always order that the Protective Commissioner supervise the manager's actions.