I have a question for Ms. Wilson -- Assuming, ma'am, that, as your book relates, poor Alexei was that brutally slain, the attempt to cremate him failed, and he was buried where he lay, how would the Bolsheviks have explained the whereabouts of whatever sister was later said to have been burnt with him?
You must be referring to Yurovsky's 1922 account of the burial in which he claims to have burned only one body, that of Alexei. He is quite clear on this point: "I ordered that we begin the burning with Alexei. We laid his body down, and soaked it with gasoline, and quickly set it on fire, just to see if it would work, since no one knew how to go about this...It was not possible for us to burn any more of the bodies, for the farmers and workers were beginning to be about..." He doesn't explain what happened to the missing girl at all, except in a very general way when he wrote that all bodies, except that of the tsesarevich, were put into the grave.
The problem with the cremation is that the accounts of it vary so very much. Some variance is to be expected, as the statements of the witnesses were given between two and forty-six years after the supposed event. And things are confused even further by statements from people who were not even on the Koptiyaki road that morning:
In 1920, Yurovsky claimed to have burned two bodies, Alexei and either Alexandra or Demidova. We know that bodies attributed to Alexandra and Demidova were in the grave, and that neither bore signs of burning/ carbonization.
In 1922, Yurovsky claimed to have burned only Alexei -- presumably the fourth daughter also went into the mass grave, which we know isn't true.
In 1934, Yurovsky was back to burning two bodies, this time, Alexei and "most likely" Demidova.
In 1932 and in 1946, Peter Ermakov claimed that all of the bodies were burned "to ash" by using "five tins of gasoline" and "two buckets of sulfuric acid." We have two second-hand account from Peter Voikov wherein he agrees with Ermakov that all the bodies were burned. If you accept that any of the Romanov bodies are represented in the Koptiyaki grave, then all four of these statements are discredited.
In 1963, Michael Kudrin claimed that four bodies were burned; specifically, Nicholas, Alexei, Alexandra and Dr. Botkin. All eleven bodies, including the four charred ones, were interred in a single grave. We know that this is not true, because two bodies are missing from the grave (and arguably, the small number of bones left barely account for nine skeletons), and none of those in the grave bear signs of burning/carbonization. Kudrin, however, admits that he was not at the gravesite -- unlike Ermakov, who gave himself a leading role though it seems most likely that in his drunken state he came and went from the site -- but claims that he heard the details from Isai Rodzinsky.