Hi, Alexander!  With thanks to Mark, and adding to what he said...   
      
   ak>  Vladimir Putin's daughter   
      
      
              Vladimir Putin = one individual.  Correct use of possessive.   
      
      
      
   ak>  Maria Sharapova's neighbors   
      
      
              Maria Sharapova = one individual.  Correct use of possessive.   
      
      
      
   ak>  volleyball player's children   
      
      
              Do you mean "a volleyball player"... i.e. singular, although you   
   may be thinking of a hypothetical individual as representative of a larger   
   group... or do you mean "volleyball players *in general*" (plural).  This is   
   significant because the correct placement of the apostrophe depends on your   
   answer....  ;-)   
      
      
      
      
   --- timEd/386 1.10.y2k+   
    * Origin: Wits' End, Vancouver CANADA (1:153/716)