Brezhnev might have been a Russian born in Ukraine (names of father and mother are typically Russian; nationality in his passport was changed a few times, depending on what was politically more convenient). Khrustchev officially was a Russian from Kursk region, but there are rumors that his biological father was a Polish nobleman from Kursk, whom his mother cheated with. In general though these people falsified their biographies to fit prevailing political winds so we might not be able to figure out who they are, and in any case Russian Empire was a melting pot, so "pure nationalities" will be very difficult to find.
How many were ethnic Russians?
Lenin: Mixed (Russian, Chuvash, Kalmyk, Jewish)
Stalin: Mixed (Half Georgian, Half Russian, native tongue and writing Georgian, studied for Georgian Orthodox Priesthood)
Malenkov (Half Russian, Half Macedonian - father was a Foreign Soldier for Tsar)
Khrushchev (Ukraine)
Brezhnev (Ukraine-Tartar)
Andropov (Half- Don Cossack Ukrainian, Half German Jewish)
Cherneko (Ukraine)
Gorbachev (Half Ukrainian, Half Russian)