Please tell me if the descendants of Darby Sullivan of Westmoreland County, VA have been yDNA tested for genealogical purposes. yDNA test results from your line which you have connected with a paper trail to O'Sullivan Beara/Bere may help the rest of us connect to one of the early lines. The results may help us to rule out O'Sullivan Beara/Bere or help us to know that there is a distinct possible connection to that line. There is, of course, the possibility that the results will not lead us in either direction.
If you are not familiar wtih yDNA genealogical testing, I can point you to some websites where the information is available.
Here's hoping that your Sullivan line has been tested or that someone in your line is open to the testing.
Thank you. Cee