Yup, the tech should say which areas. Off the top of my head, I believe its The Burning Forest, Shem, and Skinner's Roam. They are fighting with other spawnable locations, and tend to be scattered. Wiping out other nests and bandit camps can help, although I believe that you need to leave the area for the spawns to repopulate. It took me about an hour to find the camp when I was last testing it, but I upped the spawnable locations in those areas, so hopefully it won't take that long. Should be worth it when you find them, though.

are there specific locations where they spawn

Current mechanic is that the descendants spawn in a camp and join for free. Might be a bit overpowered, as the last photo shows. See everyone with a turtleneck and paints? They're a hybrid descendant that will join for free...