This is a probate question, not a family law one, so I changed that for you.
A petition for years support is common and he does not HAVE to have any other heir's consent although he can seek it. Usually, the petition means he will get property that will thus not go to other heirs.
Once he has the property he can leave it to anyone he chooses.
This answer is not intended to provide you with specific legal advice regarding your situation, or to create any attorney-client relationship.
A year's support is the right given to a surviving spouse (or a surviving minor child) under Georgia law - it is the right to an award of property from the deceased person's probate estate. The amount is supposed to be the amount needed to support the claiming person for a year after the deceased person's death. If all heirs and beneficiaries consent, then the surviving spouse generally gets whatever he or she asks for. However, if your father and your aunts want to contest the claim by your stepgrandfather, they can. If they do, the court is supposed to really look into the facts of your stepgrandfather's situation and award only what it really feels is reasonably needed for the year's support. If your father and your aunts want more information, they should consult their own attorneys to see what rights they have.
If your stepgrandfather gets an award of the house as year's support, it provides him protection against creditor claims (except a mortgage) and a property tax break for the year of the award. It is also then his property, and your father and aunts will not have any legal rights regarding his probate estate unless they are his blood or adopted children, rather than stepchildren.