Answers for "wordpress get all admin users"

wp is user admin

if ( current_user_can('administrator') ) {} // also others than admin w same capabilities
if ( is_user_admin() ){} // if it is admin
if ( is_admin() ){} //if the view is not the admin interface but the theme

wordpress get username

$current_user = wp_get_current_user();
echo($current_user->user_login);