Just before you encounter the titanite Demon, turn right, down the ladder and through the hole in the floor. Jump down onto the little ledge on the left. Aggro them with arrows and they will roll towards you and against the wall. When they stop rolling they will walk away a bit. That is the moment where you can shoot them with arrows. It took me 2 Standard Arrows with a +8 Longbow to take one down (relevant stats: strenght 33, dexterity 24). To lure the ones out that are around the corner, simply shoot an arrow against the far left wall. If you spot them shoot them and they will run at you. After clearing the room from the Bonewheels you can smoothly take on the Black Knight.
I think it would be helpful to add the information that there are 7 of them, because you can't see 2 or 3 of them because they are around the corner, when you enter the room this way.
I think it would be helpful to add the information that there are 7 of them, because you can't see 2 or 3 of them because they are around the corner, when you enter the room this way.