If you have a holy/disc priest, you should NEVER be pulling aggro from the pets until they die. Period. If you are, you're not pulling with the pets or you're standing in an AoE and, hence, Doing It Wrong(tm). :P Harsh, but them's the facts.

To recap: priest + locks strategy is:

Step 1) target a mob for each VW/FG.
Step 2) Sic VW/FGs on mobs.
Step 3) WAIT until VW/FGs cast their first taunts.
Step 4) Start dropping DPS on your first mob.
Step 5) When mob 1 dies, switch idle pets to mob 2 and continue DPS.
Step 6) Repeat step 5 for remaining mobs.
Step 7) GOTO STEP 1 (Yeah, I know. GOTO's are bad. STFU.)

That's really all there is to it. If it is a tough mob like a boss, let the VWs build a few seconds of aggro using renew/health funnel, THEN start DPSing. I've done it. Works like a champ.