Rostislav Rostislavovich and all his siblings are descendants of Ivan III and Sophia Palaiologina through their paternal grandmother, Alexandra, Princess Galitzine, and so are all living members of the House of Galitzine. This genealogy is cited on Solokov 2007 and the Russian Wikipedia (page 1 and 2)
The ancestor of all living Galitzines, Andrey Andreevich d.1638, was the son of Irina Ivanovna Mstislavskaya d. 1621, daughter of van Fedorovich Mstislavsky d. 1586, son of Anastasia Petrovna Ibragimovna d. 1541, daughter of the Khazar Prince Khudai-Kul and Eudokia Ivanovna of Moscow (1492-1513), daughter of Ivan III and Sophia Palaiologina.
