I am also researching the Heard Co, GA Daniel family. My ancestor was Littleton Daniel son of Isham Daniel of Chatham Co, NC. One of Littleton's sons David Daniel married Nancy Mathis probably in Heard Co, GA. I believe that Nancy was the dau of Isaac Mathis and Sally Daniel (Jean) Mathis. An old letter I have states that Nancy had a brother Gideon Mathis.
The widow Sally Jean was living between Littleton and his brother Jesse Daniel on the 1800 Census of Chatham Co, NC. She was probably a sister of Littleton and Jesse Daniel.
She then moved to Heard Co, GA after marrying Isaac Mathis.
David and Nancy (Mathis) Daniel named their first son Isaac Littleton Daniel, I believe after their fathers. Littleton Daniel also moved to the part of Coweta Co, GA which became Heard Co, GA after the death of his father Isham Daniel in 1819 in NC.
David Daniel moved to Choctaw Co, MS c1848 then on to Louisiana where he and Nancy died. They are buried in the Old Shongaloo Cemetery in Webster Parish, LA in unmarked graves.
The only Alexander I found in my records was the son of Littleton Daniel Jr. who married Mary Ann Peddy. This Alexander was born c1846 however. I don't know much about him.