If you play with teammates, and anyone of them dies even once, your progress is reset I had to do it solo, and kill lots of enemies with the sword, failed a bunch of times I would recommend doing it on the least required difficulty, because any small "unexpected hazard" i.e: the architects designs, can kill you

Try doing it in the whisper mission. Just get to the shadow thrall room and sit down there and farm them. Makes the whole order super easy and less annoying to worry about possibly dying during it.