Have you tried to go deeper on Amber Road? Maybe there you can see something! For example I had to go deeper for Frostford, but you can easily encounter some bystanders to rescue. You just have to be lucky unfortunately XD
And about unlocking the potential, it's different for each slave as far as I could see. For example, for two of them to make it go to the next level, I had to elevate both of them to noble; another one I had to bring with me on the "battlefield" and win a battle for making her go to the next level - you mean when you've a "+" next to the name, right? When it's like that, just talk to them, not interact. Talk. Select the first option about what need to be done for upgrading her level and the "AI" will tell you everything.
So far, I didn't see anything around the internet.