Yes, several things.
First, check the Supreme Court listing to see if probate has been applied for -
Party search. You’ll want to search by your step-mother’s name in the Supreme Court. Note that probate is not always required.
If all the assets are in your step-mother’s name and she has deceased, then the power of attorney will no longer be usable. If you want to throw the cat amongst the pigeons, so to speak, get an official death certificate and provide it to the bank. If she hasn’t advised them and is simply continuing to operate the account this should cause the bank to put a stop on the account. Be very careful doing this, because if your father is reliant on that money to survive you could be hurting him in the process.
If you believe there is any likelihood of ‘elder abuse’ then you can consider reporting the matter to the Office of the Adult Guardian, or making an urgent application to QCAT. Elder abuse can be a wide range of things, including mismanaging and/or withholding finances. While most courts and tribunals are effectively closed for hearings, this will likely constitute an urgent matter. I’d suggest contacting QCAT directly (but they will only discuss limited procedural steps, not give you any form of advice).
While your father is entitled to obtain a copy of the will and, assuming he is a beneficiary, entitled to have the estate duly administered, it is reliant on him exercising his rights should he have capacity to do so. If he does the, not only does this strengthen a case for elder abuse it also could place your step-sister in a precarious position for acting against your father’s best interests by failing to administer the estate.
It must also be considered that there may be another side to things which you’re not aware of. I’d get the full story before doing anything overt. At the very least talk to your father to get his perspective. Going the wrong direction here is the type of thing that can fracture families.