Two things that might help,
I notice your use of historical photographs as basis. You might look at Arthur Rothstein and Dorothea Lange, they took photos of people living in the dust bowl during the 30s for the FSA. The ones that aren't of the dust and devastation might work for Welkin. They've got some serious living through some stuff vibes and I would think those would fall in public domain.
Second thing. I see you don't have a lot of audio work under your belts but want to voice all of your NPCs. Consider using Audacity with your audio files. Cleaning up mic buzz (which you are going to get at different levels and are going to want at only one) is really easy in audacity. You can alter a file in very specific repeatable ways as well, in other words I would think you might be able to have someone voice multiple characters and between what they do to alter their voice and what you do to process the files differently (pitch adjust etc) you could probably end up being able to make it sound like more than one person and do it consistently.