Are children of a deceased heir in titled to a deceased's person estate if they died without a will?

My condolences to you on the loss of your father and your sister. As for your question, in Georgia, the children of a deceased child of your father would normally take their deceased parent's place as heirs. So, assuming your father had his primary residence in Georgia at the time of his death, your deceased sister's children would take her place as heirs of your father. That does not, by itself, answer the question of who receives money held in his account. The only assets which heirs of a deceased person are entitled to receive are assets which become part of the deceased person's probate estate. Only if an account was owned by your father in his sole name, with no other owners and without any "payable on death" or other beneficiary-type designation, would his heirs receive assets from that account. But if the account is part of his probate estate, then yes, your sister's children would take the share she would have received if she survived your father. I would very strongly suggest that whoever is administering your father's estate get the help of an experienced probate attorney to help with the administration.