Before the pull
You'll have to spread the healers between the 2 boss that will be tanked in an opposite side of the room.
You should also take 2 healers in center to heal the warriors on the big bugs. Those healers will ve in the middle of the room and will be able to heal right or left tanks when there is nothing to do middle.
You should use consummables for this fight that is very mana intensive.
You can also use Greater Frost, Fire, Nature and Shadow Protection potions.
The Frost damage is from the blizzard. This one is easy to avoid, because you have the debuff and animation before it actually hits you.
The Fire damage is from the bug explosion. Thiso ne is also easy to avoid, you just need to stay away from big bugs.
The Nature damage are from the little bugs if you take aggro. You can't really avoid this one.
The Shadow damage is from the boss if you take aggro. It happens sometimes, and although it won't kill you, a SR pot is a good idea.
I personally only use NR pot, because the debuff does a lot of damage and is not avoidable.
The fight
As said above, it's a mana intensive fight. Don't use flash heals, it will burn your mana. And use mana pot / runes (or lily roots) on CD. Be ready to use R5 greater heal as a proactive heal on tanks. Keep your shield for the tank when he takes the debuff.
You'll have a warrior and warlock tanks on your side to heal. You should also be in range of the warior in middle that is taning the bugs. The other damages will be blizzard or bugs aggro on raid.
The blizzard is really easy to avoid. As soon as you see you have the debuff, move. You have like 2s to do so before actually taking damages.
Try to stay away from any kind of bugs and use fade at each teleport so you don't take aggro from the caster boss and don't take shadow damage.
Keep your shield for the tank when he takes the debuff.