Ah, so this might be confusing for some people as it was for me because of the terminology. Non-Player Characters
are just that: characters which a player does not control. Typically in these types of Role Plays, NPCs aren't central characters; instead they're ancillary characters, used to help the plot along.
So if I'm understanding you correctly, if you choose to RP a preexisting Star Wars character, you must create an original character of your own and RP them as well?
I think you got your terminology mixed up, that's all.