I located the names of the two individuals in The Fate of the Romanovs, p. 300 of the hard-cover version.
"one of those who refused to shoot was,ironically, Adolf Lepa, commandor of the factory battalion; the other was Andras Verhas, a Hungarian prisoner of war. " The source is, on p. 591, "Netrebin, in TsDOOSO, f.4, op.1, d.149"
The paragraph continues: "Having been dismissed, Lepa and Verhas fled to the Popov House across Vomesensky Lane, where the battalion commander spent the night, as Guard Michael Letemin recalled, complaining about the murders."