I don't know anything about that aspect of game development, so I can't comment about it. But many games have numerous voiced characters, so I imagine it would be something similar. If it's unfeasible to give each role a unique voice, then at least players should get options for 2-3 (4-6 because two genders) voices with different personalities.
That said, story, quests, and game mechanics take priority over an aspect like voice acting.
Isn't that what happened with the case of Dragon Age: Origins?