This answer is not intended to provide you with specific legal advice regarding your situation, or to create an attorney-client relationship.
First, please let me offer you my condolences on the loss of your brother.
Assuming that your brother was a Georgia resident, and that he had not remarried after his divorce from the former wife, and assuming that he did not have any children who predeceased him but left living descendants of their own, then only the children who are your brother's children by birth or adoption would be his heirs. A person's "heirs" in Georgia are the ones who generally would receive any assets which passed through that person's probate estate if the deceased person had no will. The heirs are also the ones who typically have standing to challenge a Will if there was one and the heirs object to it.
If a Georgia resident is married at the time of his death and has no children, then the surviving spouse is generally the only heir. If the Georgia resident was married and had one or more living children (and no deceased children), then the surviving spouse and the resident's children are the heirs. It gets more complicated if there are any predeceased children who have their own descendants, so I'll stop there.
A person's children, for purposes of determining who his heirs are, are those people who Georgia law considers to be his children - generally, this means any children born to (or deemed to have been born to) the decedent, as well as any children he legally adopted. Stepchildren are not generally considered to be the legal children of their stepparent unless the stepparent legally adopted the stepchildren - in that case, however, after the adoption the stepchildren are really children. If the only legal relationship which was ever established between the deceased person and his stepchildren was the relationship created when the decedent married the stepchildren's mother, then they would generally never be considered to be his heirs under Georgia law.
In Georgia, when a person dies with no spouse and three natural children, his three natural children are his sole heirs. If the decedent father had no will, each child of his would be entitled to 1/3 of his estate pursuant to Georgia law. A step-child has no right to notice of a petition for solemn form probate or a petition for administration as a step-child who has not been legally adopted and is not the natural child of the decednet is not an heir of a decedent. Of course, the decedent can name a step-child (or any other person) as a beneficiary under his will.
Georgia provides the rules of descent and distribution at O.C.G.A. 53-2-1. This code section provides the rules for distribution of a decedent's estate when the person died without a will (i.e., "intestate"). Legally adopted persons are treated the same as natural born children. O.C.G.A. section 53-1-8 (1997). If a person is not legally adopted, the fact that the decedent married the person's parent has no effect. Stated differently, a step-child is not considered an heir of a decedent.
The specific facts of the decedent's estate must be considered carefully. Administration of an estate can be complicated and while Georgia law does not require that one hire an attorney, you may wish to consult legal counsel to assist you with the process.
THIS COMMUNICATION DOES NOT CREATE AN ATTORNEY-CLIENT RELATIONSHIP and is for informational purposes only. This communication does not constitute legal advice and may not be relied upon as such.