The Companion Management System that is native to the OC is primarily contained in a script library called ginc_companion. There are several tasks that must be accomplished in order to correctly manage your companions through this system:
Initializing Companions
Setting Spawn Waypoints
Setting Hangout Waypoints (where companions go when you dismiss them)
Spawning Companions
Dismissing Companions from the party
Moving Hangouts
Preserving Companion state while loading new Modules
Using the Roster GUI
You will need to write new scripts to perform custom logic for your own companions. It is recommended that you have a basic working knowledge of scripting before attempting to implement this system.