First, make your way up to Ranger Substation Osprey. You will encounter four White Legs guarding the prisoners. If you're a high enough level, one or more of them may be armed with and/or brush guns.
After defeating them all, (as there is no peaceful solution) you need to open the cell to free the three prisoners. To do this you can either lockpick the Hard locked cell door or find the key in a toolbox upstairs in the Ranger substation tower. Either solution gives the same amount of quest XP, excluding the bonus XP for successfully picking the lock.
Journal entries
Stage
Status
Description
10
Release the Sorrow prisoners at Ranger Substation Osprey.
20
Optional: Kill the White Legs at Ranger Substation Osprey.
30
Find the key to the cell door.
Notes
This quest is available only if the quest Flight from Zion is active; otherwise, the location will be empty apart from any creatures that may spawn nearby.
If you free the prisoners, they will help you fight the White Legs.
If any Sorrows die then you will not be able to complete the optional part of Flight from Zion.