We don't know much about them yet, but what we do know about them points to them being a bunch of girl scouts in training to become a bunch of Poison Ivies. Tycho writes them creepy poetry about them killing their parents and one of their taglines is "Mercy never grew on trees."
Thornwatch they've fleshed out a lot more since they're the ones getting the tabletop RPG/card game. I think the story is that they're Lookouts deserters/veterans and cursed. People can summon them to save them from the monsters of the forest. They made a bunch of posts about it but it's all so disorganized on their blog; they need to consolidate.
But it's cool how they came up with this cute idea and then snowballed it into a larger fantasy world.