You are assuming that we are talking about information from Sally Hemings' actual children. The Jefferson DNA samples all came from descendants of Jeffersons's paternal uncle Field Jefferson; the Hemings samples came from male descendants of Hemings generations removed from her children. So, actually, as one commentator pointed out about three years ago (in Chronicles magazine), there are not 25 possible candidates, but hundreds, not all of them white.
What that means is that there did not have to be ANY sexual connection between Sally Hemings and ANY Jefferson male, in order for some of her distant descendants to show Jefferson male DNA.
But how would such a person have contact with Sally Hemmings over a period of many years? No one has given a plausible explanation of this.
No such explanation is necessary. Your problem derives from your assumption that the hoax is true. They have never proven their case. For one example, the Hemings Party has always insisted that Thomas Woodson was her first child, conceived in Paris. Woodson was not the child of any Jefferson male. And reading the Hemings Party's claims in light of the DNA evidence, she was not monogamous (since they insist that Woodson was her child, which would mean that if there is anything to their claims, Hemings would have had to have at least one non-Jefferson lover). But then, having taken the trouble to read the article, you already knew that.
Thus there is actually only one other person other than Jefferson who could have fathered the children, his brother Randolph. But is has been shown that the dates when all these children were conceived coincides with dates when Thomas Jefferson had access to Sally Hemmings.
Not true. The claims are that Jefferson was at his estate when Hemings was impregnated. But there is no knowledge as to HER whereabouts, at the times she was impregnated. And not only did Jefferson's brother show up at Monticello at all of the times that Thomas was there, and regularly carouse with the slaves, but Randolph stopped spending time in the slave quarters at the same time that Sally stopped having children (because the widower Randolph had remarried). And eight different Jefferson males lived near Monticello.
Given the DNA evidence, which should not be taken too far, but is nevertheless irrefutable, a lot of the arguments in this article are irrelevant.
The only DNA evidence that even approaches irrefutability, is the evidence that Thomas Woodson was NOT the son of any Jefferson male. No DNA evidence has shown that Thomas Jefferson was the father of ANY of Sally Hemings' children.
Actually he could have been the child of Jefferson himself. You claim that cases of mis-identified paternity may have occurred among Sally Hemmings descendants. If you claim that a Jefferson Y-chromosome somehow entered into the putative line from Sally Hemmings in later generations, don't you have to allow that it could have left as well?
since they insist that Woodson was her child, which would mean that if there is anything to their claims, Hemings would have had to have at least one non-Jefferson lover). But then, having taken the trouble to read the article, you already knew that.
I admit that the first time I saw the article you posted, I did not read it extremely carefully past a certain point. This is why:
1. The identification of Eric Lander as a "liberal historian" caused me to severely downgrade my opinion of the scholarship of the authors. Lander is an extremely well-known scientist and is someone I have dealt with personally in the past. He clearly is a brilliant guy and not someone who is known for his politics.
2. The article makes the a priori assumption that saying that Jefferson may have fathered a child by a slave is merely an attempt to degrade the achievements of Jefferson. I don't think it is necessary to look at it that way. We already know that Jefferson owned slaves despite being the author of the phrase "all men are created equal" and having considered the justice of abolition. We already know that he was a complicated person, at once a very great man and a hypocrite.
3. The article takes a somewhat racist tone at certain points and overstates the possible political motives of people who have believed in the Jefferson-Hemmings link. "The Jefferson-Hemings hoaxers seek to steal America’s history, and replace it with a counterfeit version, in order to oppress America’s white majority." There was already a long-standing rumor that Jefferson fathered a child by his slave. Then DNA evidence appears that does not confirm this but shows that it is possible. It is to be expected that many people will leap to the simplest conclusion without looking at possible complexities, even if they have no political motive. Another factor is that concluding that Jefferson fathered children with Hemmings simply makes a better headline than saying that this is not quite proven. Newspapers and scientific grant seekers both find hype quite useful.
Having said that and having now read over the article you posted as well as the Nature article by Lander and Ellis, I will say that despite the heavy tendential tone and some factual errors, the authors in the thread article make a lot of good points. Lander made a mistake by allying himself with Ellis, who is highly controversial on his own. As a colaborative work their commentary article is uneven, sometimes not going beyind the evidence and in other places making an assumption that the case is proven. The article does speculate in one paragraph on the relationship with another case. "Politically, the Thomas Jefferson verdict is likely to figure in upcoming impeachment hearings on William Jefferson Clinton's sexual indiscretions, in which DNA testing has also played a role. " This may have been a true statement, but it doesn't seem too appropriate for a scientific journal, even as commentary. (I'm not how much of the article I can quote as it seems to only be available online by subscription.) The Lander and Ellis article does mention some important evidence which is not covered in the thread article: "First, several of the children bore a striking physical resemblance to Jefferson. Second, Sally's fourth child, Madison, testified late in life that Sally had identified Jefferson as the father of all her children."