I'm in the same boat. I've summoned numerous people and even together we just get overwhelmed. I burned all my weapon buffs (resins) along with all of my Human Effigies. I've probably fought them about 40 times at this point and I'm no closer than I was 4 hours ago.
When I take it slow,eventually too many of them spawn to keep up with. If I try to single them out and try to focus them down individually, I end up getting crushed trying to get to the one I am working on (they seem to hide in the back and blow fire).
All of the other bosses have been manageable but this one is a fucking nightmare.