I think I have discovered a possible connection between the artist Kalmakov and Nabokov and/or his family, to wit Gumilev. At least, see article in the Garland Companion, we know that Gumilev was important to VN. And at least one of Gumilev's books of poems (Shater ca 1921) was "decorated" by Kalmakov. Whether it is possible to retrieve the story behind that collaboration and how the Nabokov family might fit into it - well, I'll keep you posted of any future discoveries - not that anyone besides myself has shown the slightest interest...