Eldin hides in the rear end of the carriage between a a couple of the shelves with crates held in them. It appears to be a flawless hide attempt.

INITIATIVE TRACKER

Am I able to take Carrick’s turn right now?

Majin will get somewhere he can see into the carriage with the guards. He will take 2 shots one for each of them, aiming to hurt not kill so non-lethal

Attack: 19 Damage: 6 Guard 3

Attack: 12 Damage: 11 Guard 4

Majin climbs between carriages 2 & 3 and fires two shots that echo as they fly into the back of the guards, giving them a nasty wound each. (Grunt #3: 12 damage. Grunt #4: 9 damage.)

INITIATIVE TRACKER

As a Bonus Action, Carrick is going to use Second Wind to try and regain some HP.

Second Wind:13

Then he'll make two non-lethal attacks against #3.

Attack: 16 Damage: 13

Attack: 25 Damage: 15

If the two grunts are still standing, Boo will use her action to make two non-lethal Eldritch Blast attacks, one beam 15 to hit 5 damage if hits at #3 and the other beam at #4 11 to hit 5 damage if hits and with her bonus action to use her Healing Light to restore 5 HP to Carrick.

Carrick, with some swift blows, manages to knock the grunts out. They crumple to the ground, their batons clattering to the ground as the lightning charge disappears. Boo, you may redo your turn if you want to.

INITIATIVE TRACKER

(Are we still in initiative)?

For the time being, no. If we need to jump back into initiative, I'll just use the same results, as this area can be conceived as one big encounter.

The sleep spell will wear off in less than a minute though, so up to you what you do with that guard...

Can Eldin do something now?

As mentioned, out of combat rounds for now, but will put back into it if needed.

In that case, Eldin will suggest someone tie up and gag the sleeping grunt (He gave his rope to Boo). In the meantime, he will look around Carriage on to see if there are any crates that might contain dragon shards. Using Cunning action and Mage Hand, Eldin will be able to look through two crates at once, provided they aren't locked.

Perception: 10 or Investigation: 11

Carrick will tie up the guard and shove some cloth into his mouth. 

Sure, Carrick could you make a Sleight of Hand check?

The crates in this room all seem to have markings with crate numbers placed upon them. Eldin notes there is a clipboard stashed to the side that seems to have a list of the boxes and begins cross referencing them with the boxes. He recalls that you are looking for a crate that should not be listed on the cargo. It'll take a minute or two to check all of the containers in this room.

Would Carrick have advantage since he's trying to tie up an unconscious person?

Just a flat roll, please.

Since Eldin finds a list, he can cross reference it. Is any of the boxes in Carriage 1 out of place (not just because numbers but for other reasons as well)

Sleight of Hand:23

Boo will quickly move down an join the others, seeing everyone busy she takes a look at Carrick with her Healer's Kit and restores 15 HP plus as a bonus action will use her Healing Light 8 HP to Carrick. After seeing to Carrick's injuries, Boo will then do a medical check 10 on all the Cannith grunts to ensure they are alright and not in need of healing, or medical attention, etc.

The fourth grunt is tied, bound, and gagged before he has a chance to wake up. As he does he begins to struggle somewhat at the restraints. (He can be knocked out with a quick chop or bash to the neck/head if wanted)

Eldin sees that all the crates in this room appear to be in the correct place.

Boo determines that they have all been dealt with in nonlethal measures, and are not going to die from their wounds. Some may have some bad concussions for a few hours afterwards, but nothing too long lasting. 

Carrick has his wounds tended to by Boo. (Carrick: 51/54 HP)