I know that my great grandmother was Elisabetta Sergeevna Meshcherskaya. Her fathers name (my great great grandfather) was Sergei Meshchersky. And her mother's name (my great great grandmother) was Ekaterina. I also know that Elisabetta Meshchersky married Micheal Kousminsky (Tatyana Behr's youngest son.)
There was a Prince Sergei Borisovich Meshchersky (b. 4 November 1852) who married Princess Ekaterina Semenovna Abamelik-Lazareva (b. 20 Aug 1856) in 1879. I don't know if they were your ancestors, but their children would have been about the same age as Tatyana Behrs Kuzminsky's son, Mikhail; he was born ca. 1875 and died ca. 1938.
Good luck with your research!