Michael (II) - aka THE GREATEST CSA-WINS LEVEL CLICHE OF THE RUSSIAN ALTERNATE HISTORY (sadly unappreciated here).
George (I) - died of tuberculosis, less used than Michael for obvious purposes, etc.
Those are the guys most frequently used in Russian TLs for alternate successors. A large TL on George (I) I had seen even had Russia still launching the first man in space, and the surname is Gagarin - the difference is that's His Serene Highness Prince Gagarin, commander of Royal Cosmonaut Corps.
http://fai.org.ru/forum/index.php/forum/101-миг/
MIG/WEG -TL (World of Emperor George) - yes, big TLs get their own subsections on Russian AH-board. I'd recommend this one, as despite it devolving into sort of wank and puns as it approaches mid-XX century (and thus may be non-"edible" for Google Translate), it's non-cliche unlike the f*ckton of Michael ones.
The PoD is Borki tragedy gone wrong (and differently) - George survives by miracle, basically, Alexander III is dead and Nicholas is paralyzed. And one of co-authors of the TL also happens to be senior manager of Wargaming, company of World of Tanks/World of Planes fame.