In North Carolina and in my opinion, Payable-On-Death accounts pass to the named beneficiaries listed onthe account if they survive (in this case) your grandmother. You indicate that your father and aunt were the named beneficiaries. If they were named as tenants-in-common (for example, 50% to each), then your father's share should pass according to grandmother's will if she left a will, or by your intestate laws if she did not. You aunt survived your grandmother, so her share of the POD accounts would pass through your aunt's estate. However, there may be beneficiaries named as follow: "equally to my son and my daughter, or to the survivor among them." In this latter case, the entire amount of the POD accounts would pass to your aunt.
Your question is just way too non-speific in the information you give, for any clear answer to be provided. If bank accounts have pay-on-death designations, then the owner of those accounts, following your grandmother's death, will be determined by those designations, and not by any proivision in her Will. I can't tell from what you write, just how those designations were written, and if indeed these accounts were held in trust with your grandmother as trustee, and if so what what the terms of that trust were. If you are the persoanl representative of your father's estate, and you have your "Letters of Administration" you should be able to get the bank to show you any title documents and pay on death instructions signed by your grandmother, that left anything to your father.