Creating new user on xubuntu can be done through the command line, as long as you have root permission (sudo) you can create a new user on xubuntu.
You can use 'adduser' tool for creating new user on xubuntu, simply type adduser followed by the name of the user you wish to create.
sudo adduser [username]
Example:
sudo adduser john
sudo adduser erin
sudo adduser michael
To confirm the new user you just created, you can logout and then see on the xubuntu login screen, the new user should be shown on the dropdown user list on xubuntu login screen.
