From the book "The Romanovs" by Lincoln: post abdication he has the IF reading "The 3 Muskuteers, The Scarlet Pimpernel, as well as books by Turgenev, Tolstoy Saltykov-Schedrin. Other sources have Alexanadra reading Anna Karennia. They also read Greenmantle by John Buchan (which is online) Then there is the Russian 1905 best seller "The Duel" by Alexander Kuprin which Nicholas heard about but I don't know if he read it since it is a less than flattering portrayal of the Russian armys officer corps.
The book "Romanov Autumn" has this to say on GD Serge A. He was a well read man according to one german prince who knew him. He knew all the great Russian writers of his day. Also when Tolstoy wanted to get Alexander III to pardon the assassins of Alexander II he gave his petition to Serge. The account of him supposedly forbidding Ella to read Anna Karennnia comes from Paleogue diary which may have just been him repeating gossip.