(Slight sigh) I assure that you can fight 3 death knights at the same time and not take a single hit on your characters (level 17).
The one key to an easy victory is always the same - lower rsistances and blind/stun/knock down/freeze whatever.
The first round of any serious fight should see your group doing nothing else than taking opposition figures out of the equation temporarily. After killing them one by one while holding the others in place.
To be honest - the death knight fights in Phantom Forest were among the easiest of the whole game.
Regards,
Thorsten
