Another thought, Benjamin D Johnson appears to have been the oldest son of Harris.
The 1840 census finds a Benjamin Johnson, head of household and the 1860 census finds a Benjamin Johnson in Middle Division, Chatham, NC born NC about 1780. This was same location of Harris and family in 1860.
Benjamin's wife was Isabelle born 1785, Eli Johnson born 1820 and David Johnson born 1842 in household. Benjamin Johnston is in the 1820 census as head of household.
You have to look at a blank census form to understand how old and sex to determine males to females and ages as there is no indexing at top of the page.
Interesting note, there were two John McIver's ? on this page next to each other the enumerator noted the first one as "little" and the second as "big"
Happy Hunting !