Should you choose the Claws in Baxter's Propaganda - you'll become a member of the group, allowing you to complete missions for additional reward by working counter to the Berserkers. Here's a quick Thieving for Yasma Mission guide.
Your mission is simple - steal each item requested from members of The Berserkers, drop it off in a dead drop location, and collect your reward from the reward chest. You'll find the missions in the chest behind Yasma, and the rewards in the chest in the other room.
Thorhild's Valuables Mission
If you have level 2 lockpicking, you can easily open Thorhild's Chest, otherwise, you can find the key in her hut without much issue. Snag the Fertilizer and drop it off, then collect your reward and complete the next missions.
Scrappy's Valuables Mission
If you haven't completed "On The Road to Becoming a Warrior" - the best time to do this mission is after that, as Scrappy will be away at the mine with his (easy lock) chest wide open to being pilfered. Head to his hut, snag the figurine, and drop it off for some easy EXP and Elexit.
Tilas' Valuables Mission
This one is pretty tough since Tilas is almost always in the room, but the code to Tilas' Safe is 0000 if you can stay hidden long enough. If you're doing the Berserker's faction quests - wait to do this one until you have "An Antidote for Tilas" as he'll be out cold and you can easily get into the safe without being spotted.
Fenris' Valuables Mission
Now we get to steal from Fenris - if you loop around the back of his house, and approach from the northeast, you can easily sneak behind him and open up the safe. The code is 8696, and you can snag everything inside.
Once you've completed all 4 submissions, it's time to head back to Yasma and have a chat. You've hit all the core people at The Fort, now it's time to hit Rat himself.
Rat's Valuables Mission
This is a tough one, with a few different components. First of all, you'll want a level 2 pickpocket skill, which you can learn from Tjark, in the Claws area near Yasma. Then, head up to the upper fort and use the (if you did the Fake Berserker Quest) now-empty home of Ejnar to sleep until midnight. Head over to Rat, and jump up behind him to pick the key from his pockets and take his valuables out of the safe, as seen below:
With the first Blood Pacts book in hand - now head back and sleep until Morning. This is where you have to go extremely slow, or you'll be easily detected. Make your way to the downward steps, while Rat sits on his throne. Then, rather than walking down, you'll need to stutter step - stop, go, stop go, and take a hard right past the bottom to get to Rat's safe. The code, unless you want to hack it - is 4781.
Head back to Yasma, to not only blow her mind - but complete the mission. Have one final chat to complete Thieving for Yasma, and then you can go on your way - while still being able to make it to Warrior and Paladin rank in The Fort. Head up to Rat, and you'll even find he's sending Berserkers to find his lost books.