On the basis of the documentation I have seen, it is probable (based on age and reported place of birth) but not proven, Stephen F. Box (b. abt. 1770 in SC) and his brother, John Morris Box (b. Aug. 7, 1780 in SC) were in the household of Robert Box, Sr. in the 1790 census of Pendleton Co. SC and their brother, Robert Box, Jr. was also in the census with his sons, John Box (b. 1787) and Robert Box (b. May 13, 1789). The Edward Box who was also in the Pendleton Co. census is believed to be brother of Robert Box, Sr.
This is a documented Robert Box, Sr. but it is not proven (although I believe he is) that he is the son of Robert and Phillis Box. I believe he is the Robert Box, Jr. who appears on several Laurens Co. SC deeds with Robert Box, the elder.
Jonathan Box was listed in the 1790 census of Laurens Co. SC in the vicinity of Margaret Box, believed to be the widow of Joseph Box (Sr.). That is the basis on which I have considered him as a 1st cousin of Robert Box, Jr., Stephen Box and John Morris Box.