You are making a serious error in logic here. We only have evidence for one of Sally Hemmings children, Eston. We do not know the father of the others, except that a Jefferson did not father Thomas Woodson. Since two of the children had different fathers, how do you conclude that the others had the same father?
Of course there is also Randolph's proclivity for fraternizing with the slaves:
Isaac Jefferson, in his "Memoirs of a Monticello Slave," as dictated to Charles Campbell, made the following statement:
"Old Master's brother, Mass Randall[sic], was a mighty simple man: used to come out among black people, play the fiddle and dance half the night; hadn't much more sense than Isaac." (JB p 22)
My sympathies are with your family as you deal with both the reality of some connection and the calumny heaped upon your most distinguished family member.
I am assuming that all of Sally's children had the same father, true (I will get to Woodson in a moment), simply because almost all accounts assume she did (or maybe two at most). Certainly, those who sought to clear Jefferson would have pointed out that she slept around if she did- she was a black woman and a slave, and if it were true it would been in their favor to do so. Also, it seems to me that she would have had more children if she was with lots of men- she had, if I recall, six in a period of eighteen years. And again, she only got pregnant when Jefferson was around, despite the fact that during this time he was hardly at Monticello as Sec of State, VP, and President. Now it is possible that she was pregnant more times and suffered miscarriages- but it seems funny to me that babies who made to birth were all conceived while Jefferson was around. In my opinion, Jefferson (Thomas or Randolph or someone else) who she was with was probably the only man that fathered the children, but there is no definite proof. As for Woodson, when I did research on this topic for a school paper sometimes before the DNA results, I read about Woodson. We know that Jefferson fathered Woodson but we assume that Sally mothered Woodson. In fact, there is no evidence of a slave in Thomas Woodson (or Hemings) at Monticello born in 1790. Jefferson kept excellent records on his slaves (which how we know when the other Hemings were born) in his Farm Book, yet he is not in the book. In addition, Madison Heming's account indicates that the baby Sally was carrying upon her arrival in Virginia from France died at birth or soon after. So there is a serious question, IMO whether Woodson is Sally's son.
Unfortunately, we cannot test the other children, since the test requires a unbroken line of Y-chromosomes. Of the five children commonly discussed, Woodson, I already talked about, Beverly and Harriet (as a daughter, naturally there is no Y-chromosome to test) passed for white as adult so their descendent believe themselves to be white and probably have no clue about being a decendent of a black slave. Madison lived as a black person, but his Y-chromosome line was extinguished generations ago. (Although, as the article points out, they still could test the body of his son). Eston also passed for white, but the Jefferson/Hemings story remained in their family so they were easy to find.
Sorry for the long post, I just love history and I am only my vacation from law school, so forgive me. The whole topics is interesting to us, because it is an historical mystery and because to 21th century society, it contains two of the major obsessions of our time- race and sex. But certainly true or untrue it could never diminish the accomplishments of Thomas Jefferson- those are far too important and stand the test of time, long after people stop caring about who he slept with.