Usual Brit pronunciation is LEN-in. (Same as if you knocked on your mate, Leonard's, door and asked his mum if he was there. )

But my Russian History teacher always used the proper Russian pronunciation, so I have no problems with vika's (kerrect) pronunciation. (And isn't it Ul-YAH-nov?)

As to river Lena, vika, I'd have to see it written in cyrillic before I'd know if it was Lyeh - nya or Lyeh - nah.
(I remember that the "Le" is Lyeh, but can't remember the rest!!).

Incidently, why did L.D.Bronstein choose his pseudonym?