Although it is not currently the most fashionable biography, I urge you in the strongest terms to read the Dumas Malone biography of Jefferson. It was written before political correctness. As long as you understand Malone will give Jefferson the benefit of the doubt, you will get a great deal from it, as the scholarship is first-rate and Malone is remarkably fair. Every one of the more recent treatments of Jefferson I have read, from the excreable Fawn Brodie on, has had a real axe to grind, and is hence unreliable.
Too bad the DNA excluded both Peter and Samuel Carr! Randolph Jefferson was barely mentioned prior to the DNA test as a possible father. In order to determine the father, you must look to see what Jefferson Y-chromosone holder was there at the time of each Hemings child conception- so far there is only one who was there each time- Thomas Jefferson. That, along with exclusion of the Carr brothers who were the most likely suspects prior to the DNA test, leads me to believe that Jefferson was the father of Sally's children. Of course, no one can ever know the truth.