You could have the people doing the roleplaying, but then you would have to put it into a script form, perhaps have a narrator for scene changes and to help describe some of the action. But you would need voice actors with decent mics (the ones that you use to play WoW or for skype are not good enough, sorry), sound effects, background music, mixing equipment, etc. 

I have done and mixed audio productions before in the past as well as fandubs, demo reels, etc. Same with the voice acting thing. I still do it on a rare occasion. Your best bet would be to let the roleplayers handle the writing/roleplaying and if they have an interest in acting their character (assuming it fits) or another one, give them a chance if they are a good fit. Otherwise I might suggest going somewhere like the Voice Acting Alliance forum which has a lot of people that do this for a hobby and they have tutorials and the like to help you out.

I guess I can be a source as well since I been doing it on and off now for 15 years. Yes, that long. Just seems like yesterday too.... 

*departs for a trip down memory lane*