The slimes don't do anything except cast a stacking debuff if they're not eaten by the slugs. Ideally you should gather all the slugs, mark one to be damaged, and do whatever you can to hold them on you. Everyone except MT should be stacked on you for Acid Rain (which spawns the slimes) so they're close together when they spawn. Everyone runs out of this, focuses down the marked slug, then the weak slug should eat all 3 slimes. (make sure you don't kill the slug before it eats them) After the slug eats the slimes you have about 10 seconds to kill it or it'll blow up and wipe the raid. OT will need big heals through this (or you could use Hallowed Ground as mentioned above) and ideally you'll have your melee DPS LB it.

After that, my group typically has the OT stack behind the boss and we'll have our casters AOE the boss and the other two slugs down, then focus on the boss. If you get a second set of slugs your OT needs to pick them up and hold them until the boss is dead.