For your double mage problems, there are three things you need to do. I've played some Priest/Warrior in the past, and let me tell you that combo is even more vulnerable to double frost mage, heh!
1) Positioning - Both you and your rogue partner must correctly position yourselves to make use of line of sight. When you see that they are about to unload their giant burst, CloS and ducking out of LoS, Shadowstepping to you (and you are, of course, right next to that pillar) will all save you. You have course should try to be in a position where you can heal without being counterspelled or polymorphed. More subtle though is that your rogue should not chase a mage into a position where he forces you to expose yourself or reposition dangerously. The damage you do to the mages is permanent, you can take your time with this team.
I know this may seem obvious, but both the mages and their pets are so dependent on LoS that abusing it is really your best answer. So when in need, "pillar hump" away!
2) Displ - It's a pain with Winter's Chill but since Dispel Magic is two at a time and Mages have no resistance to dispelling you should try your best to spam Dispel on your Rogue in between PW:S/PoM/Renew CD/Duration. Their burst damage relies entirely around shatter and its requisite novas, so if you can remove them quickly it's fairly game breaking. Then just save the cooldown effects and LoS for when you do get counterspell silenced or polymorphed at a bad time.
3) SW

- Ideally you've positioned yourself so well that you never get polymorphed, but obviously that can't happen and sometimes you'll have to run out in the open while repositioning or to fear. I'm sure you're familiar with Shadow Word: Death and breaking Polymorph, but in this setup especially it's very key as it's the only CC they have. If you cancel the first polymorph and, the 5 and 2.5 second ones are much less powerful in putting you behind on healing. You can also save your trinket for when they inevitably counterspell silence and then polymorph.
Also, not really an important thing but Water Elementals have barely any mana, 2 mana burns many times will make them completley OOM, so if you have nothing else to do (unlikely considering the healing load and dispelling the rogue and the mage he's attacking) that's an option.
For the Rogue/Warrior I think you just need more gear to survive through the stuns. After that the rogue can help peel them off of you and you can fear the Rogue.