Having two avatars sounds like you just have it creating two players? When you hover over the play-in-editor icon, see if you have the number of players set to 2. Usually if you do this, UE4 opens a second window for the other player.
As for C++ vs Java, to be honest with you, I have no idea. About which one companies prefer, both are rather good languages imo.
I just seriously wish C++ would implement some form of reflection (RTTI does not count) already, it’d make a lot of things much, much easier.