rainbow 6 vegas 2 co-op question

[smith1080p]

Ok i'm new to the game. Me and my girlfriend both have user names on my ps3..well we wanted to play terrorist hunt or the story together on the same ps3...we both created characters...can we use them together?
When i start the game it only lets me use my created player...same when she does...When you join it doesnt give you a option that i can see to use the other persons character....or other words use them both together...

Is there anyway to do this??? We both used are created characters on the first one together. That i can remember....Thanks any info or help is appreciated