There are different mail addresses, users access their accounts via separate Roundcubemail installation.
Why I can't see their sent messages and other folders in cpanel, at this moment I am able to view only incoming mail?
Check that you have subscribed to all of there folders by going into settings folders.
Well, I guess, I have subscribed to the accounts -
(http://i45.tinypic.com/2rrqe1d.jpg)
But it doesn't show any subfolders.