Juliette - sorry to hear about your headaches.
But please understand that a power of attorney for property becomes effective the moment it is executed for the purposes stated in the document. In fact a power of attorney CEASES to be effective when the donor becomes incompetent unless the poa expressly provides that it continues to be effective during incompetency. I urge you to review this with your lawyer.
People grant powers of attorneys for a variety of reasons. Some poa's are for very specific purposes. You spend your winters in Florida but need to sell your home in Ottawa in February. Instead of flying back and forth, before leaving you grant someone a power of attorney solely for the purpose of doing everything necessary to sell your home (executing a transfer/deed etc.).
Most poa's are general and give the recipient the power to deal with all of someone's property. If someone is in a body cast or has difficulty getting out, a poa would allow someone else to take care of that person's finances.
And just because you start using a poa doesn't mean that Tom no longer has power over his finances - he still does. A poa does not remove the donor's right to deal with his finances - it just gives someone else equal rights. Only when a court declares Tom incompetent would he lose these rights.
You need to advise the bank and any other financial institution Tom deals with of the situation NOW - show them the poa and ask them if this will be sufficient to deal with Tom's finances. And this is not a decision for a bank teller or clerk - but a manager in consultation with a legal department.
If you wait until Tom's competency is in question and your documents are found to be deficient - it will be too late to fix it - and you will be sol.
Please look into this asap