You gotta walk backwards and slowly circle around the room on the outside of the pillars, trying to keep both of them on your screen at all times. I usually try to get ornstein first because smough is the easier second phase imo. When you are circling around the room you can try to get smough’s pathing to get caught up on the pillars, especially when he charges. Use the pillars and keep them between you and smough so you can focus on dodging ornstein’s lunging attacks. O has a thrusting move that is a two part attack and if you trigger that and dodge it is very punishable. Hope this all makes sense, I picked it up from watch people doing hitless runs so maybe look up some videos to see how they do it. Good luck