Flight from Zion
You'll start off with Joshua Graham as a companion, just outside of the base. Note that he offers some great bonuses to .45 pistols, so consider switching to that.
This is actually a really short “battle." Most of the efforts are around the edges of it. If you look in your pip-boy, you'll note that you have 3 different side quests. They're spread across the map, so let's start with the closest one. You don't have to do these side quests, but doing them gives you a happier ending.
Walk forward and then up a slope to the right to approach Ranger Station Osprey. There are three White Legs standing guard. There should be a mix of shooters and melee fighters, so just move up with Joshua and gun them down with whatever you have.
You can either loot the key from a toolbox, or just pick the lock with 75 points in Lockpick. Once you set the Sorrows free, the quest will finish.
Move along the road to reach the East Fork Bridge. In order to retake the bridge from the White Legs, you basically just have to approach them with a .45 pistol drawn. Between Joshua and you, you should basically lay out a sheer wall of bullets that kills everyone on the bridge in a few seconds. Once they're dead, the quest will complete.
For the Sanctity of the Dead quest, jump off the bridge into the river and swim toward the marked bank. You should see two Sorrows waiting by the river. Talk to the one named “Dancing Flame" to learn about it. He wants to push forward and kill the White Legs on their burial mound, but he's probably a little outgunned.
With 75 points in Speech, you can convince him to just run away and forget about the White Legs. You can also convince him to just hang back and wait while you and Joshua handle it. That will buy you a little time to charge in and handle the White Legs.
There seem to be 4 melee fighters at the Burial Mound. The biggest threat to Dancing Flame will be the men with the shishkebabs. Target them first. The Sorrows should be able to handle a few with their Yao Guai gauntlets, especially if you can draw some fire onto yourself. Advance and take out the sniper, and you'll be able to finish up the quest.
Once that's done, you can move toward the Pine Creek Tunnel. Push past the battles along the road between the rear guard and the White Legs. There should just be a few pairs. Help them finish the fight and move forward until you find Daniel and Salt-Upon-Wounds.
If you have 75 points in Speech, you can convince him to just leave. The reason doesn't matter, except for roleplaying. If you pass the Speech check he'll agree to walk away.
if not, then you'll need to kill him. There are a few other White Legs around, Walk backwards and fire at them to pick them off and clear the battlefield. If any Sorrows survived on the way toward the tunnel, you can fall back to pull them into the fight and give Salt-Upon-Wounds an extra target. Other than that, just get some distance, go into VATS and put a few high powered rifle rounds into his head. He has a ton of HP, so try to VATS to take half off, then just do hit and run attacks to take him out.
Once you're finished, just use the detonator to seal the passage and finish up the game.