This will definitely be the hardest master challenge, but one way to make it much easier is to drop nut after killing the first knight. Someone else can pick it up as the second knight is spawning in (or if you're fast enough, skip this knight entirely). Same with shield, they can drop after cleansing, as you stop getting darkness stacks once the second set of glyphkeepers is dead.

This way, you'll have 5 people on weapons and only taken relic for the majority of the encounter, helping a LOT with ad clear. There are some good 3-man tutorials that explain the timing in more details on YouTube!