Walkthrough
Finding Moe and Marley
The quest marker doesn't bring you to where the two skags are but instead the general area where they can be found. You may need to look around for a little to find them, which however shouldn't be hard at night since Moe is a giant flaming skag.
Fighting Moe and Marley
It's highly suggested to take out one at a time, considering their size and strength. If you are having trouble killing them straight on, have Moe chase you to the first building you passed on the way up that had bandits. The bandits may have respawned and if they haven't they may soon, causing the skags and bandits to fight each other. Meanwhile you can run in the back of the house where there is a hill. Walk up the hill and jump on the roof. From here you can shoot down on Moe during the battle. This may take a while at low levels. Once Moe is dead, and the other small skags are for the most part also dead, taking out Marley shouldn't be too hard, just time consuming if you're doing it alone. Running back to where you found Moe, look for Marley. She's just a large skag, no fire. Just shoot her from a little bit of a distance because her AI isn't too smart and she shouldn't attack much.
Turning In
Once you have killed both Moe and Marley, it is recommended to do the other quests in the zone. Then you can go back to the bounty board to claim your reward.