I didn't find anything that positively connects him as Albert's son but I believe he is. Are you saying that Lizzie wife of Albert C is buried in Irwin Co.? I didn't have that. I followed John Walter's children on the census. I also figured that Albert C and family moved on to Texas and that Albert died out there. Maybe both John F and Albert C had planned to go to Texas but John F stopped because his 1st wife died.
The only mention I have of Agnes is from the Elbert Co. land deed that mentions her and also the Greene record.
There is a sign on the property that was Dr. John's stating that was the house site. I took a picture of the sign. I also walked some of the land looking for a family cemetery but no luck. I haven't seen any pictures of Dr. John. He is mentioned in Sherman's records and in a report of persons living in that area during the Civil War.
Send me your email and I will send you the picture of the sign.