Yeah, it will almost certainly be Charles Evans Hughes, who will most assuredly be alive. (Unless Salvador decides he dies, but honestly, after two reasonable deaths, throwing a third one in for lulz would be a rather silly move.)
If Knox dies on schedule--and there's no reason he shouldn't--then Harding will get enough of the Presidency to probably send him off at about the same time. At which point the Secretary of State becomes President #3 in the chain.
Right--the name's likely to show up, because the Buonapartes were fond of it, but his OTL father is probably a genetically similar but not identical individual living in Corsica, and his OTL mother was never born, and her family lives in Genoa now.
Even Catherine needed some level of popular sentiment against him to move. If that isn't there, her scheme becomes too dangerous to be practical, and likely unwinds in the opening stages, making it easier, not harder, for Peter to remove her.