>I wish to contact the decsendant(s) of Prince Felix Youssoupoff and Princess Irina Youssoupoff.
I assume you mean Felix Felixovitch, Prince Youssoupoff, Count Soumarokoff-Elston (1887-1967) - a co-conspirator in the murder of Rasputin - who married in 1914 HH Princess Irina Alexandrovna of Russia (1895-1970), niece of Nicholas II, Emperor of Russia.
If so, Prince Felix and Princess Irina had one child, a daughter named Princess Irina (1915-1983).
In 1938, Princess Irina Felixovna married Nicholas Dimitrievitch, Count Cheremeteff (1904-1979). This couple in turn had an only child, Countess Xenia Nikolaievna Cheremeteff (b. 1945).
Countess Xenia married in 1965 Elia Sfiris (or Ilias Sfyris, Sfiri, or Sfyrias, depending on the genealogical source) (b. 1932). Once again, an only child was born: Tatiana (b. 1968).
Tatiana married in 1996 Alexis Giannakoupoulos (b. 1963). I am not aware of any children for this couple.
Finally, it is my understanding that Tatiana and her husband, and her parents, Elia and Xenia, live in Athens.