A bit late on this thread - I know. Isaac/Naimbana are my great-great grandparents. I have the Isaac/Naimbana Forbes family bible dated mid-1850's.
(1) The bible outlines a family tree that goes back 3 generations prior on both sides!
(2) I have been to the Washington Grove grave site and the Isaac Forbes who married Naimbana died in 1863. I suspect there are two different Isaac Forbes in play here - probably related.
(3) Another more controversial bit of information is that Naimbana is an African name - and it is not clear from descriptions (even Hodges' will available online) that Naimbana's mother is married to Hodges - perhaps there is another "Mary".
My big question is: Did Isaac T Forbes marry Hodges Gallop's illegitimate daughter with an African name? Is that why this branch traveled to IL? etc....