Use a Warlock or Hunter and blink jump to escape the crystal chamber shield. Kill the first sword bearer before your fire team exits the chamber and a second sword bearer will spawn allowing your team to attack Crota with TWO SWORDS. You can also just use this technique to one down Crota before your team exits the main building.
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Here is another video I just did showing what happens after you blink jump out. Nothing gets spawned outside until "something" passes through the doorways on the left or right side. I verified this in another test where I lured one of the knights out through the door. You're pretty much all alone with Crota and one sword bearer until he enrages.