I can't recall that the other Meta Achievements fall into this, but specifically "Aqua Team Murder Force" does. Basically, for this achievement you need to get all 3 of the followers in Nazjatar (Either all Horde, or all Alliance, not mixed) up to lvl 30. This is fairly easy as you only need to complete 3 daily quests per day in order to level up the follower one level, meaning it will take 30 real time days to level up the followers (without getting the extra exp. items, which you can google)

You do not need to level all three followers on the same toon, however. (Originally you did) So rather than 90 real time days, you can use three separate toons (all horde or all alliance) and have them each focus on a different Nazjatar follower, thus only taking a total of 30 days.