You do know that using an estus will heal the phantoms that are helping you right? Nothing is worse than helping someone kill a boss and that person not healing once even though you are fighting the boss at half health for over a minute already. Those are pretty much the only times I ever get really frustrated at the game.
Also, I managed to find someone online to help me with O&S. He even dropped a much better catalyst for me to use - there are some really cool people in this game. Real shame he died before I finished the boss - realyl wanted him to get the humanity for it.