Rodger-
I think perhaps the answers to your questions are resolved by looking at the situation of the Ural Regional Soviet and Ekaterinburg. The Ural Soviet wasn't a tight, "famously ruthless, methodical, and motivated" group of Bolsheviks-they were hanging on to power by a thread, faced with evacuating the Urals, and caught up in in-fighting and conspiracies that summer of 1918.
As a member of the Cheka, and a more fiercely determined man than Avdayev (who flat out refused to go along with the idea of killing them and even tried to object before the event-hence his removal as commandant), Yurovsky was perhaps the best they could get. They did have people around with experience in murder-like Ermakov-but the last thing they wanted, after the breakdown in security and thefts-was to put an irresponsible person in charge. Yurovsky may not have been the ideal choice but he was their only choice given the circumstances.
You have to remember, too, that before his appointment Yurovsky was full of the usual revolutionary bluster and revenge, which may have gone a long way in convincing them he would be up to the task. After he spent time among the Romanovs, as he wrote, he had a different view and this made the murder more difficult, but he carried out as his "revolutionary obligation" if you will.
I seriously doubt that any of the men in the Ural Regional Soviet had much idea about the French Revolution or Robespierre with the exception of Peter Voikov-they were not, on the whole, highly educated nor politically experienced or widely read. They were men caught in the middle of the Civil War fighting for their survival and convinced that Moscow didn't know what was going on.
As to the issue of bombs versus guns: during the captivity in Ekaterinburg, there were a number of shots fired accidentally by guards-none of which got any attention in the city, whereas when one of the guards dropped a grenade the story about a "bomb" at the IH spread like wildfire, with tales that Alexei had died "of fright." Having no practical experience, I'm sure Yurovsky thought guns were the quickest and safest option-especially given throwing bombs on the first floor, with exposed walls and an open window, versus a volley of guns in a semi-basement room where the walls were twice as thick as above. He expected it to go easily-they'd be shot, they'd die, and probably no more than two dozen bullets fired. But with no experience he didn't anticipate what would happen.
Incidentally, of the 103 possible shots, we calculated-based on wounds, statements, memoirs, forensics, and recovered evidence-that something like only 50 or so were fired-half were not, owing to the smoke and the chaos. The only witness who recalled hearing the shots remembered them as "indistinct" and "muffled" owing to the thickness of the basement walls.
Greg King