NCSA Telnet for Mac intercepts certain control sequences -- by default, ^C, ^S and ^Q. When you press ^C do you see the message [Interrupt Process]? That means telnet is intercepting the ^C key.
The solution is easy, but far from obvious. In Telnet, go to the Session menu, then to Setup Keys.... There will be three boxes there with control key sequences in them. Delete the contents, leaving the boxes blank. Telnet should now behave.
Then from the File menu, select Save Set so you don't have to do this every time, provided you logon by opening the set file, not simply opening telnet and typing in a hostname.
No. If someone else wants to access Chebucto Community Net, they must get their own account. If they just want to explore, they can log in as "guest" (lowercase, no quotation marks) and try the system out.
Never allow any one else to use or know your password. Your password is the only thing protecting the confidentiality of your e-mail and other files.