MC fight on the Instructor. 25 Naxx

Angusilla here, offering my 2 cents worth on the Instructor Mind Control fight. Feel free to ignore this but I have done the fight several times. It can be really chaotic but if the raid group goes at it with a plan it can go well.

The complexity... read: pressure .. for the priests is obvious. But good Offtanking of the two extra adds helps.
What I have seen work well is for an AOE tank (Paladin or Death Knight) to hold the two extras off to the right hand side. There is an impulse to take them back away from the fight but then they are too far away for the range of the priest's Mind Control.

Part of the function of this holding pattern is it provides a place for the priest that has just been relieved of tanking (who needs to drop MC, then reaquire his target) to trot his subject to ... hopefully the Consecrate or Death n Decay will pick up the mob while the priests casts his MC for a fresh round. If the OT is aware enough he can actually taunt or even chain the released mob, really securing it until the priest reaquires his target.
Otherwise these freshly released apprentices can run amok for the (hopefully) brief time until they are again subject to Mind Control. They can get into the healer-caster group, or go after the priest that's just been in control and is currently pressured to retarget and then cast Mind Control for another round.

For the priests, starting at the top of the ramp, wait until the instructor has paused to talk to one of the two apprentices at the far side of the circle. At that point, the two priests each casts Mind Soothe on their respective target. They can then move to the bottom of the ramp.
The Mind Soothe prevents the two targeted apprentices from aggoing, while the instuctor and the other two are out of range and unaware.
MC is cast and this is often when the Instructor and his two apprentices from the back of the circle will aggro. While the two MC"d apprentices begin to tank the Instructor, the designated AOE tank moves through and pulls the two loose apprentices to the right hand side, taking care not to move too far away from the bottom of the ramp.

Priest A begins, with bone armor up, by taunting the Instructor. How long he needs to hold the Boss, I am unsure about. But after perhaps 10 seconds, maybe 15, Priest B taunts the instructor to him.
At this point, priest A moves his 'pet to the AOE tank and releases. Hopefully that apprentice will stay with the tank long enough for the priest to quickly recast MC.

It helps for the priest to have his assigned target for MC all ready up as his "focus" so that grabbing the target for quickly recasting the Mind Control is smooth. He then moves back to the boss, popping bone armor as he moves. Once in range he should Taunt, announcing on vent to Priest B that he's taken over.

Priest B then does the same cycle...move 'pet' apprentice to the AOE tank, release, target and reaquire. Then trot right back to the boss, popping Bone Armor on the go, and picking up the Boss immediately.

Communication back and forth between the priests is vital. Also, just as quicly as the apprentice can be released, retargeted, MC'ed and moved back to pickup the boss creates a steady rhythm for the two priests to alternate.

Honestly, it get really hectic, and often doesn't run so smoothly but this is the pattern that I've seen work best.
Others have their ideas. This is what has worked for me. My Shadow Priest is Buktwild on Vek Nilash... I've done this fight many times.
Honestly, it's really unusual to find two priests that have done the fight often enough to not be all tense and awkward. The pressure is tough... the success of the event rests with them but other factors can contribute to the potential success.

Also, there are times when a controlled apprentice will die. This is another reason to have the extra apprentices tanked close enough that they are easily in range for either priest to target as an alternative. The cooldowns on Bone Armor can also be an issue. Should there be a mix up and one priest needs to taunt but cooldowns are not ready, just release the apprentice and quickly grab an alternate and carry on.