It seems that you want to know if it is possible to set up multiple accounts in order to use the same Slingbox.
As a matter of fact, it is possible. You only need to create every account as usual and add the Slingbox. However, the Slingbox will allow only one connection at the time. This means that it will allow only one user (when in use).
The following thread will allow you to get further information and steps to follow.