I agree  with Galben we need him alive to interogate.  Whoever attacks next go for a knockout punch not a head cleaver.

By my count, Klarg has 4 hp left. If Jake or Bearkiller want to try to get down the chimney successfully and make an attack, you can do so - otherwise, you can go the long way and wait until next turn.

Jake runs through the waterfall room, using his action to dash to approximately the suspended bridge by the stream.

Bearkiller jumps down the chimney but lands awkwardly (8 athletics roll = 4+4). He is able to get up to try and grapple with Klarg, but is unsuccessful with the unarmed strike (1d20+4 = 6)

Klarg swings his mighty morning star toward Galben, swinging wildly as Galben quickly ducks out of the way (8 to hit).

Next turns can be taken in whatever order you are able to post.

(Galben rises back up after nearly taking a a hit from Klarg, He aims his arrow at Klarg looking to knock him out, not take the life out of him)

(Damage roll 15+5=20: Piercing damage: 1+3=4)

(Galben released the arrow as Klarg turns to run and pierces him in the ankle causing him to trip and hit his head on a rock. Knocking him unconcious)

Klarg lays at your feet, unconscious. Jake enters the kennel cavern and the party regroups.

Jake pulls some rope from his pack and starts binding the bugbear's limbs.  "Watch him closely, we don't want him getting loose." He then uses his medical knowledge to stabilize Klarg and wake him up. (medicine check, 18+5=23)

OldMan digs through Klarg's belongings and pockets if he has any (probably wearing rags) looking for loot and/or anything useful.  Using his dagger he also cuts a chunk of hair from Klarg and puts it in his pack.  It may prove useful later.

Ok gang we obviously want to get info from this guy and we need to continue to investigate this place but we also need a rest sometime so I can study and get some of my better spells back in mind.  Also we have injuries that need tending.  How is everyone feeling?  What's our play?

Bearkiller will take a short rest and try to regain his strength. As athletic as he thinks he is, that last tumble got to him. He’s not getting any younger.

"A rest seems wise. I will keep watch while the rest of you heal up and study" 

(Long rest is what we need to take I think to get your spells back)

(Galben takes up a position near the opening of the side cave entrance)

I would not recommend that we take a long rest in enemy territory. (Also it's still just mid-afternoon and typically long rests will be taken at night). Regula sits down and starts tending his wounds.

Anyone taking a short rest can roll their hit die to regain some hp. Also, what questions do you have for Klarg as he starts groggily coming to? "You petulant swine. [spits blood at your feet] How dare you tie up Klarg!"

Jake patches himself up as best he can during a short rest.  Abysmal die roll on healing.  "These goblins were nasty.  I hope none of us catch anything from them.  Btw, OldMan, did you find anything interesting on Klarg?  Does anyone else want to go check out that store room, see if there's any good stuff in there?  Grab any rations you may find, and anything else you think is of value. I'm strong, I can help carry once I catch my breath." 

(Galben looks at Klarg)

Where are Gundren Rockseeker and Sildar Hallwinter?

(Persuasion Roll:16+0=16)

OldMan's Investigation check 6+4 = 10 probably didn't reveal much if anyone else wants to poke around in the bleeding carcass of a goat turd.

FYI everyone I am pretty strong for a wizard if anyone wants me to carry items too.  

 Intimidation check 20+3=23

"Look Klarg we know you kiss King Grol's backside like it was a horny Bugbear *****.  And we know Black Spider paid you to capture Gundren Rockseeker.  We know you took Rockseeker to Grol.  So you are no more than a delivery goblin for the top powers.  You have no one who cares if you stay alive so you need to give us a reason to keep you alive.  If there are more goblins we will kill them just like all the others.  We are good at that as you have seen.  Tell us about the human you have.  Tell us what Grol wants with Rockseeker and the lot.  The more you tell us the less blood that we drain from you over the next hour."

Bengal tiger mentioned to me that I should clarify that I rolled a natural 20 in my previous post so yeah I got that going for me.  If Klarg isn't scared of me he should be.

Seeing things well in hand, Thallan investigates the bridge, holding just short of the tunnel. (Perception 5+3=8)

Begrudgingly, Klarg starts to answer your questions: "Klarg did as instructed, delivering that worthless worm Gundren to King Grol at Cragmaw Castle. The Black Spider sent the order but Klarg has never met him. Klarg does the bidding of the King and only followed the orders given. Gundren's pathetic companion wasn't part of the command, so he's tied up in the Golbin Den in the eating alcove across the bridge. Klarg has no idea what they wanted with these two pathetic creatures. You might as well just kill Klarg now because once Klarg gets loose from these restraints, your puny bones will become toothpicks!"

Klarg does not have anything on his person other than the hide armor he is wearing and the morning star he carried in battle. OldMan's hunch that Klarg is merely a middle man seems to be playing out as expected. His knowledge about the machinations afoot are very limited but he sees himself as something of a local warlord. Bound, he's harmless, but you also are not sure how long you'll be able to hold him as he becomes more agitated.

Thallan does not see anything out of the ordinary at the bridge - it leads off into the darkness to the west as has been described by the various goblins interrogated. Did anyone inspect the supplies as Jake suggested?

(Galben takes the morning star weapon from Klarg and takes it into the cavern of the cave with all the supplies and puts it next to the short bow and scimitar)

He starts looking through the supplies. (Investigation roll: 8+0=8)

As noted previously, most of the supplies and crates are marked with the image of a blue lion—the symbol of the Lionshield Coster, a merchant company with a warehouse and trading post in Phandalin. Thallan would have known this given that he was sent out to the party from Phandalin and could share this information with the group. The captured stores are bulky and you will have to carry them back to the wagon for transport.

Hidden among the stolen provisions is an unlocked treasure chest belonging to Klarg that contains 600 cp, 110 sp, two potions of healing, and a jade statuette of a frog with tiny golden orbs for eyes. The frog statuette is small enough to fit in a pocket or pouch but the remainder will need to be loaded into the wagon.