hello bob, first of all im not sure if you mean 3xlock 2x shadow priest or 4xwarlock 1xshadow priest, or you actually mean 4xlock and 2x shadow priest which would mean 6 characters so you would create for yourself a few problems with leveling a 6 man group not impossible but not easy or effective.

fist of all dont confuse shadowweave as a pvp set its far from it, the bonus is sadly not good enough for pvp, if it was for pvp when this set is intended for pve then they would nerf it.

On all acounts stay away from shadowweave for pvp whereever possible, it lacks the basic stats for pvp, stamina and resilience. you could socket these true, but then it defeats the purpose of this set, its for you to bridge the gap alot easyer to collect raid gear from instance gear.

if you check out the priest forums sadly shadow is a pve build right now its seriously lacking in pvp, compared to disp spec priests. They need some serious changes to be made more useful in pvp, its not that they cant pvp, far from it they deal insane damage, can heal when needed, shields, dispell, burn mana, fear... the list goes on priests are insane, this is why they are targeted very early on in a match and you cant really miss them they stand out like a sore thumb in an arena or battleground, they lack defenceive skills which means they drop very fast when focused. So at the moment i think any team with a shadow priest in it needs another healer to keep them up as they cant expect that VE no matter how good is going to keep them allive. For pve they are awsome crazy mana batteries, 1100 spell damage shadow priest shouldnt ever really go oom.

I can see why your considering a shadow priest to what it brings to the fight for warlocks namely a 20% buff in their shadow dps when you add shadow weaveing maxed and misery debuff together. 20% isnt really worth the loss of the healing, and you could heal but its alot of fiddleing about for the priest to shift in and out to heal even more so if they are being focus'd. Specing the warlocks like i listed above should give them plenty of healing back from drain life, your deep demon locks lack siphon life which means that if focused you would need to heal them more than the SL/SL ones, but the beauty of haveing 2 of each spec is to the untrained eye would be very hard to determin which ones which.

Consider this set up as
SL/SL locks are your tanks as they will still do the most damage but they will also handle far more damage than your deep demon locks.
Deep demon locks, these are effectively here for some AI abuse, the Felguard is insanely clever in a small area like an arena, leave charge on auto and i will constantly save your ass, also stick it one on a healer and leave him their, this will stop the healer ever running out of combat and drinking saveing you a whole lot of issues. Any clever arena team will counter this by killing your felguards and felhounds, no problem just get them back into combat, that 3-6 seconds per pet that the team have to work that out and start beating on them should give you a large enough window to drain down someone on that team.
your priest is the groups healer, use your aoe fear spareingly, more than likely someone either a warlock priest or warrior is going to make up atleast one of the members in the oposeing team, so they will charge in and try to aoe fear to scatter your group a well timed offensive aoe fear will save you from that.

This team and setup with priests and warlocks is a drain team, your main objective is not really to nuke down someone as aff/demon locks cant nuke (nukeing really implies that you could totally destroy a target who potentially has over 13k hp so fast that the oposeing teams healers couldnt manage it), and i wouldnt advise destruction for pvp, mastered its not bad, but then you need to build your team up to comensate for the destruction warlock, much like a team with a shadow priest needs to. So your goal is to put enough pressure on the oposeing teams healers to keep them healing on demand and consantly forceing them to drain all their mana.

You priest should really be only topping off your warlocks hp when ever needed or if they are focus'd start throwing out flash heals on the warlocks.

Alot of people who have played a 4 warlock and priest may disagree with alot of the points and talents ive posted above thats fine, this is just my own experience as a solo lock and solo priest, i did put alot of thaught into this sort of boxing group before decideing what i was to do.

here is what i would spec my priest like

http://www.wowhead.com/?talent=bxMGkhMZfVtccMoVhAo

this build would be pretty much the best thing to go for while you are collecting gear and in the lower rateings this would be fine.

when your fully geared up with some 12k hp 400 reslience and 1500 healing.

http://www.wowhead.com/?talent=bxMGkGMtrcqtfmt

somthing like that will offer you plenty of offensive as you will have to expect any team with brains is going to focus your priest. I would choose disp over holy in higher brackets as your priest will end up doing most of the 'tanking'

noone as of yet does a full arena team as it makes things very dependant on reaction times, i think this team set up could do it becuase of how clever the ai of the felguards are. they bring in some very clever aspects to an arena.

note also how i always take one or the other on the talents which give an effect on takeing a critical blow, this is becuase it will only proc one of the effects at a time, you dont want blessed recovery procing when you could of had focused will on you instead, and spell warding is a grossly underrated talent and i wouldnt spec away from it ever for pvp.

personally i went druid shaman team makeup becuase i want the ability to nuke a target rather than drain, the problem with a full drain team is its going to drag out the game alot longer, the longer your match goes on for the longer your giveing your team to think and adapt to your teams makeup give them long enough and they will counter you. You can only apply a instant dot once every 1.5 seconds, thats pretty much 3.5 seconds per target, then you have to refresh dots when removed and when, paladins, mages, warlocks, priests, druids can all remove your dots they are going to get removed. does make the fight drag on alot more.

no expert on 5v5 4 warlock 1 priest arena teams but thats the problems i could forsee giving this team less of an edge than say a shaman or another burst team makeup. I wouldnt like to say that this team wouldnt work becuase i honistly think it could do, but would take maybe 3 times longer than a shaman team would be to learn properly. Shaman are pretty simple you have really 3 offensive skills, lightning bolt, chain lightning and a shock, 2 are on cooldowns of untalented 6 seconds, so pretty much leaves you doing, LB LB LB CL SHOCK LB LB CL SHOCK sort of combos, not as simple with a warlock.

i think this team would do well because of the load of damage puts way way to much pressure on the oposeing teams healers. it is a pretty insane drain, and would love anyone who takes this into practice to film it and post it on the forums for others considering this build to get a taste of what to expect.

lastly any shadow damage team running into a destruction lock is going to have to wand them to death or expect them to be immune to every spell you throw at them, from you constantly procing Nether Protection, as far as i remember has no internal cooldown, at least it didnt when i had my distruction lock in 2.0

sorry for the long post but had alot to say on this team makeup as i was seriously considering it for a long time, i just hope that some of it was useful to you.