I think I have a farming route for these guys that works pretty well. Starting from Ringed City Streets, enter the area requiring you to "show your humanity". Then kill the two Ringed Knights there (and the giant, if you want), then go down the stairs near the giant and down the ladder. From there, if you look down, you should see two Ringed Knights below you, one of them close enough to the wall to get a plunging attack on. Do that plunging attack, then take them out (the second one won't aggro unless you get in his field of view). From there, get close to the edge opposite the wall you just dropped down, and you should see another Ringed Knight. You can perform a leap attack that will turn into a plunging attack onto him, then take care of him. Then use the coiled sword fragment/homeward bone/ dark sign and start over. It sounds complicated, but once you get it down, you can get through the route pretty quickly, and it feels safer and more efficient than farming the four on the sunken building in the swamp.