No, the problem isn't that they're essential. The problem is that neither of them can be harmed, at all, by anyone. And none of the console commands work on them, not one.
Ah I see what you mean.
But how on earth did they start brawling in the first place? That should be impossible. I smell Mod problems.
Blizzard Battletag: UnderDog#21677
Shepard: "Wrex! Do we have mawsign?"
Wrex: "Shepard, we have mawsign the likes of which even Reapers have never seen!"