2 ways to start the fight, wait and let them come to you or you moving into open as a "bait" for their CDs. If you wanna try to bait them make sure your in range to use demonic circle. If they pop cds and try to burst you down just teleport to safety and let their cds Tick out. If they try to rush past you to kill your shaman try to fear one of them while riding past you. Teleport back, silence one of them with felhunter followed with fear, change target to other Mage and fear him. Now both of the Mages Should have used trinkets, and Shaman should hex one of them. Between the start cc cast corruption, agony and siphon life on both Mages.

Save Howl of Terror for Mirror images (and aoe silence if your a Blood Elf)

Have your pet dispel on manual so you can remove sheep from you or your shaman.

Important against this team is well rotated CC, fear followed fear since they have so many ways to get out of the fears, idea in this is to buy your shaman some time. Not long after silencing, fearing and hexing the Mages should start being quite low health, at this point they most likely will try to retreat and evocate. DO NOT let this happen.

Use of fear:
Cast fear on Mage 1, instantly cast fear on Mage 2.
Mage 1 trinkets out of fear, cast fear on Mage 1, Mage 2 trinkets out of fear
Cast fear on mage 2

Use of silence:
Instantly silence on of the Mages if he gets in range with your healer, since arcane Mages hardly use.
Cast time spells this days, so only idea is to slow hes dps for 3 seconds.

Shaman:
Your shaman should try and purge arcane power of the Mage while hes in fear.