I highly recommend dotting / putting pets on the pets. The healers seem to heal the target with the lowest total HP that is missing some hp, which is almost always a pet. Here's the healing done by target breakdown for our kill last night:
Thrakgar - healing done by actor:
Thrakgar 56588 100.0 %
Erin Misthoof - healing done by actor:
Cat 295600 80.2 %
Treant 54148 14.7 %
Zhaagrym 12690 3.4 %
Thrakgar 6268 1.7 %
Liandra Suncaller - healing done by actor:
Zhaagrym 1428330 42.4 %
Cat 845364 25.1 %
Erin Misthoof 205482 6.1 %
Thrakgar 183517 5.5 %
Ruj'kah 130080 3.9 %
Narrhok Steelbreaker 126079 3.7 %
Gorgrim Shadowcleave 120589 3.6 %
Harkzog 114203 3.4 %
Liandra Suncaller 112518 3.3 %
Treant 56247 1.7 %
Maz'dinah 42562 1.3 %
Kill order was Resto Shaman (Thrakgar) --> DK --> Resto Druid (Misthoof) --> melee --> ranged --> Holy Paladin (Suncaller)
World of Logs - Real Time Raid Analysis
We had an aff lock dotting both pets, a shaman flame shocking a pet, and a couple pets on their pets.