At least in the case of KQ8, it is confirmed that Roberta at least wrote all the text in the game apparently, she also chose the actors. So as as far as story goes it is all hers. Even if it may not have been the full extent of the story as she originally wanted to tell..
Infact she had at least three different versions of that story, or at least backstories for the playable character.
See KQ8 deveopment page over on the wiki.
BTW, I think Interaction Magazine suggests that she basically let Lorelei Shannon take over KQ7 as she was busy working on what would become Phantasmagoria at the time...
Last edited by BagginsKQ; 06/01/2012 at 07:11 am.