Hi,
ok now I have understand.
You have set in Easy Profile the option "Login Type" to "Email" so Joomla Username is hidden because it is no more useful for registered users (and you can't change it).
Of course you can change the name of user and the name users can be duplicated (but it will not be useful for login).
You can see in backend that users with same name will have a different username.
see screenshots
Ad 3. Okay, so maybe exist any possible way to editing only kunena profile on site? Now when I click on kunena profile "Edit', it redirecting me to easyprofile. Maybe this way? Or it's not possible too?
Hi, this depends from Kunena, it have a plugin called "Kunena - Easyprofile Integration" (Components->Kunena->Plugins), this plugin is not developed by us, anyway try to see options from this plugin.