The default Ares database includes several guest characters, Guest-1 through Guest-4, each with a default password of ‘guest’.
You can rename these guests to whatever you like. The game looks for the ‘guest’ role, not specific names.
Four guests should be sufficient, but if you find yourself needing more, you can add new ones simply by assigning a character the ‘guest’ role. See Roles tutorial for more information.
If you remove the ‘guest’ role from all the guests, you can effectively disable guest logins, but this would be pretty extreme.