What are the names written on the back of Yuri Nazarov's photograph?
Your guesses are correct. Some of the Cyrillic letters here are written in a strange way: nobody writes ш ("sh") on the second line in this way. The letter и on the third line  has an underline that doesn't really belong. Abstracting away such gratuitous elements, I think the fourth line is "Миша" (Misha, a masculine name) in which the two middle letters are distorted with extraneous pen strokes. The full text for completeness: 


  Иванов
  Наташа
  Юрий
  Миша
  Балкутск 1951


Presumably, the photograph depicts one female (Наташа) and two males (Юрий, Миша), with "Иванов" being their last/family name. (Actually, in Russian the family name would be written in plural form, i.e., "Ивановы"). Балкутск being the town where the photo is taken in 1951.