how could it be anyone else, the match is perfect, names, ages, place of birth and residence, ethnic origins.
So Aleksei and Maria weren't divorced by 1941, as she seems to have applied for survivor spouse benefits. Why a biological child would be left with neighbors, yet continue to bear his birth name, is beyond me. It might have been a formal adoption and young Igor might have unofficially restored his original surname when taken from the streets in 1941, but it sounds so far fetched. The family which took care of him seems to have means and connections, but just leaving a child with good rich neighbors can't explain why the biological parents were cut off..
(And the story of Igor's schooling paints his childhood as far more privileged than normal. A kindergarten, in the 1930s! A specialized school with small classes and foreign language program! That's not how the toiling masses lived, I tell you. Perhaps the Kiev oldtimers can find you the special English school at Podol, or the Staro-Vedenski / Vedelsky lane, but one crucial thing you already got: grandfather's name in Novozybkov, and Alexei's year of birth)
PS: fill an online affidavit for the victims of the Nazis for Alexei at Yad Vashem now that you know his bio. And for you dad.
