• You need 3 things to be able to do this, all of which are super easy to get your hands on. The first is any sort of bow that fires regular arrows, i suggest buying a shortbow from the undead male merchant in the burg.
  
  
• You'll then want around 100 standard arrows, you don't need that many but i like to have a stock of them incase i ever do need them.
  
  
• And lastly, the trick to this whole guide, are the poison tipped arrows you can get off the female undead merchant in the tunnel, that links firelink shrine and the depths. You'll only need 4, but incase you miss an arrow or accidently use one, i personally buy 10 of them.

Your ingame equipment screen should look like this:

• Here is the location that people dread, just down this ramp is 2 of these greatbow archers and 2 of the lightning demons waiting in ambush. You must first take care of the 2 demons otherwise you'll never hit the 2 knights.
  
  
  
  
• Lure the 2 demons like this and it makes them easy to kill, if you take damage just back up the ramp and pop an estus.
  
  
  
  
• Once they're both dead, you'll want to hug the far RIGHT of the small area, in the distance you should be able to make out the 2 knights, waiting for you to get on the small walkways to knock you down to hell. Your character should be in roughly the same position as shown here:
  
  

Ok, so now you're sitting in the back of the small tower, holding your bow and both types of arrows out of their sight range so you're safe from their arrows, now what? Bow's in this game have a limited range so you'll do no direct damage to the knights, however, the arrow will still travel and connect with them.

• This is where you use your standard arrows to guide your poison ones, you fire until you get the angle right and you can see when your arrow connects as there's a small buff of blue looking smoke. Once you see this puff of smoke, fire again to double check that it's there.
  
  
  
  
• Then without moving your aimer at all, swap arrows to the poison ones and fire 2 shots. This will cause the knight to become poisoned, do this with both knights then just wait for them to die off the poison damage.
  
  
  
  
  
  
• You're done, you killed the 2 Greatbow Archers without them even knowing how they died, feel free to walk along the once dangerous path to the fog gate and bonfire!