You know what if you look back at the Yussupov line, you can see that the men in family had an eye for beauty. Zenaida's mother was a beauty as was her grandmother.
Zenaida's grandmother, Zenaida Yussupova ( Does anyone know if Zenaida was named after her paternal grandmother, and her sister named after thier mother? Just a random question.)
I think it was only natural that such a line of beauty would eventually produce the lovely Zenaida and handsome Felix.