The above mentioned book "The Burning Tigris" does mention Turkish officials being tried for killing Armenians shortly after WW I. Also note there were alot of reports in the European press in the last half of the 1800s about Turkish cruelty in the balkens towards Christians ect. No doubt young "NickY and young "Alicky' read or heard or read about them while growing up. As for the Young Turks AKA the Committee of union and Progress they raised more than a few eyebrows in pre 1914 Europe do to their criminal behavior. Nazis, Facists and Communists acted in a similair manner post WW I. Nicholas, Alexandra, and even thier daughter Olga read about them. No doubt like millions of other people in Europe they thought such a gang will never take power in their country!
Among the witnesses to the Armenian genocide are US diplomats and missionaries (the US never decared war on the Ottoman empire during WW I), British POWs, and German and Austrian military personel, civilians, diplomats ect. i believe General Erich Lundendorff discusses this in his memoirs which is on the net. There are Turks today who will tell you these massacres did happen but only off the record since if they say so in public they run the risk of be jailed for "insulting turkishness" or something like that.