So let's presume that we should resolve the matter of whether Israel had a first wife (we won't necessarily have to prove her name or marriage date, but let's at least see if we can determine if he "did" have a wife and maybe if he had children prior to 1814). An 1810 Census would help for this, as we should (in theory) be able to get a count of household members. I did find one from 1820:
"United States Census, 1820", database with images, FamilySearch (ark:/61903/1:1:XHLT-HXC : Wed Mar 15 14:20:07 UTC 2023), Entry for Israel Blackburn, 1820.
Israel has a count of 1-2-0-0-1-0 and 0-0-2-0-0-0 That would be 1 free white male (FWM) under 10, 2 FWM between 10-16, and 1 FWM age 26-45, and 2 free white females aged 16-18. If we try to line this up as best we can with the records of who is said that were his children, by 1820 we would have:
Margaret (born 1800, would be 20 years old, possibly married and no longer living at home), John (born 1802, would be 18 years old, again possibly married and no longer living at home), Enos (born 1807, would be 13 years old), Margaret (born 1812, would be 8 years old), Martin (born 1812, but accounts say he died 1813). So we should see approximately 1 FWF aged 20, 1 FWM aged 18, 1 FWM aged 13, 1 FWF aged 8. And unfortunately, none of those line up at all. It sort of appears that he has children living in the household, but it's 1 boy under 10, 2 male teens aged 10-16, and 2 female teens aged 16-18. And no wife, unless one of the older teens happens to be his latest wife (considering he's 48, having an 18 year old bride wasn't unheard of, but maybe slightly unusual). And again, if he started having children as early as 1890 or 1900, at least the age of the children is within his age range to have kids.