its a bug i did that quest at 30 ish with a pretty good setup still one shot me they hit with a missle or something that hits anywhere from 1100 hp - 1990hp as far as i noticed as far as this quest go you can kinda buged them if u get a quick jump roll backwards on the pillar or behind wall then you can kinda single them out or try using dragon stone to port to tower and back that also un bugged it for me. I also noticed this will happen randomly as where sometimes you roll right on through them and other times they roll you
