From talking to Zalid, it might be worth a note to the healers about the main sources of damage, and what's important (and crucially, what's not important).
You'll have one tank on Sul full-time, and also Malakk most of the time. This tank will take the most damage, but it should be relatively steady.
Your second tank will be on Marli all the time, and taking Malakk for short periods to avoid the MT getting stunned. This tank will take steady hits of magic damage throughout the fight. Ideally, it'll be a DK or warrior.
Whenever Malakk gains a buff called "Frigid Assault", he'll start applying stacks of a debuff to his tank. In addition to debuffing them, this also does LARGE amounts of frost damage. For this reason, tanks should always use a CD, and you'll need to keep them close to full health. At about 12-13 stacks, the OT will pick up Malakk and start taking big damage.
When Malakk is empowered, watch out for Frostbite. The affected person should run straight to melee, but they'll need a quick heal on the way. Once they're in melee, there will be small-ish damage spikes on them and the melee, but these can be slowly healed up, there's no risk of imminent death.
The rest of the time, he'll be applying Biting Cold to players. This needs careful attention; its a LONG frost DoT. It can be removed (and should be) with immunity effects like Divine Shield. If it can't be removed, it needs quite a lot of healing, especially if it's coupled with another source of raid damage, such as Kazrajin's empowerment, or a Sandstorm. During these times, always prioritise the person with Biting Cold.
The rest of the raid damage is light, and can be healed effeciently. As long as sand traps are dispelled fast, they don't do significant damage. Both sand traps and biting cold will only ever affect one person because the ranged and healers will ALWAYS be spread out.
When Kazra'jin is empowered, he'll reflect some damage back at DPS players. This isn't high damage, and as mentioned is most dangerous when coupled with another source of damage, such as biting cold or a sand trap. The rest of the time, HoTs and steady, cheap healing will compensate for the damage.
Finally, there's sandstorm; this does moderate amounts of raid damage. What's most important is that you use a threat dump as soon as Sul casts it, to avoid getting killed by the adds. Then use your raid CDs such as Dev Aura and PW:B (on the tank and melee) and simply heal through the damage. Again, pay special attention to anyone with biting cold, and the tanks.
TL;DR: Malak's abilities, on both the raid and the tank, need very quick attention. Dispel sand traps and stay spread, and you can use cheap, efficient and slow heals to deal with all other sources of damage. Use raid CDs for sandstorm.
Hope that helps!