At the risk of sounding sacrireligous, what on earth is there to say about the OTMA clan ? They died before they HAD a biography, for heaven's sake. Lots of pictures perhaps. Some notes from other's diaries and memoirs and of course the de rigeur Anastasia chapter. I suppose some innocous lettres & diary enries.
If this fellow has been working on it for a number of years, it must be a longer research project than their unfornate lives lasted.
Of course, it will sell, at least to the niche market.