Perhaps it would be wise to understand that DNA is another tool for genealogists that can give us clues, but is best used in combination with traditional research.
My line happens to be one from the Henry Isbell that you mentioned that matches with the James Isbell line in the Isbell Surname Project.Through the paper trail, I have proved my line from vital records, court records, and obituaries, etc.By this I mean that I used the genealogical proof standard for conclusions and analysis.I do not copy trees without checking sources.I always try to view the original record of a document for context and clarity rather than relying on indexes and transcriptions (which are great too; as an archivist I prefer originals).So not only do I have the documents for my lineage but now I also have the science of DNA to confirm it.
Since I can prove my line, it would be interesting to see if the other line can be proved through the paper trail also.This would help determine the probability that they are two family lines with the same DNA OR not. It is possible that Henry and James were twins. It is possible that there was an honest research mix up or an adoption or foster situation with the James Isbell line.We don't know for sure.
I also had a deep clade test done on the Isbell DNA, which places it in Scotland/Ireland according to the SNP map at SNPedia.org.The defining SNP was L21 and the map distributed the SNP per 1000 matches which covered Scotland and Ireland.Compared my Isbell DNA sample to those in the Ireland Project and found it to be more in line with South Irish.Now I also know my Isbell line is Scots-Irish or Irish and can put the French Hughenot or French tradition to bed.
Thank you for highlighting DNA testing on the forum as we will be able to determine more if others test.