Speak to Jacob the Chemist and tell him you don't like the super mutants. He will tell you to break their friends out of jail. Go there and wait. Eventually, the super mutant standing guard will wander towards the door. At this time, you can pick the lock of the cells and free the two convicts. You can also steal the key from the guard, and use it on the door when he leaves. Either way, you have to wait until the guard leaves to free them, as when the nearby guard stops you. With a high enough Charisma and Intelligence (both need to be 7), the main guard can also be convinced to give the key and the prisoners can leave freely.
Once you receive this quest, you can instead turn Jacob in to Marcus for 2500 XP. Alternatively, you can perform the break, then turn them in to Marcus. Jacob and his wife will end up in prison after a fade to black screen.