How wide are these tunnels? How many people can walk there side by side?

The smaller tunnels are two people across.

Svartalf the Battlemage scans over the entire, slightly chaotic situation while hefting his trusty War Hammer - The Pulverizer, magically imbued to smash through any armor or shield without issue. Clad in his Mithril Chainmail and a variety of defensive spells (Dispel Magic, Reflect Missiles, Reflect Spells, Magic Shield) and his one favorite offensive spell, the Fireball at the ready, he assesses the situation.

The sounds coming from the middle grate are definitely not a good sign and it would be prudent to get as far away from here as possible as fast as possible. Some fools, ignoring the obvious danger, descend upon the chests like locusts, greed suppressing any concern for the slowly but steadily nearing danger. Let them lose time, effort and potentially their life.

Counting the members in the groups around the tunnels, he notices that there are 13 other individuals near the South tunnel where he is currently standing. Overall, he sees a pretty likable group with the exception of a single filthy Drow. He also spots several other dwarves. A Warrior, a Thief and even a Cleric. As a Battlemage, he feels that if him and these individuals banded together, they would complement each other quite well, covering a wide array of skills.

After a brief introduction, he extends and offer to the 3 other dwarves to create a party (Thulgrun the Warrior, Max son of Fulvus the Thief and Babargh the Cleric) hoping that as usual, the dwarves will trust their own kind and face the dangers together. He also mentions the smaller tunnel which seems to run parallel with the main South Tunnel but still remains uncertain whether or not it is worth exploring.

SmartyFartBlart, the slightly fanatical Paladin is already shouting things about smiting evil and being a "shield against the darkness" in a true Paladin fashion. He said he would guard the tunnel. But Svartalf likes his quick call to action and so far, he is the only one from the group who seems interested to begin the journey as fast as possible by suggesting that a thief scout the tunnel for traps. He seems decisive and quick to act, all good qualities in a fight and thus, Svartalf also extends the offer of partying up to him.

TLDR:
I offer to:
Thulgrun the Warrior
Max son of Fulvus the Thief
Babargh the Cleric

and

SmartyFartBlart the Paladin

to party up. If they do not decide before it is time to move, I will take their answer as a no.

Thanks. That's a relieve.

Sorry, I was too slow with editing my question above and I have almost no experience with RPGs, so I don't really know what to make of all those races, so:
Anything I should know about Haflings? Like, what does dexterous mean? (I'm asking here, beause maybe other Haflings may want to know too.)
Thanks for your patience.

Four chains, you say?

The Queen of Souls must be upon us.


Chain
Chain
Chain
...
Chain of Fools

While I, SmartyFartBlart the Human Paladin, would prefer to wait and assess the situation in the chamber, the chains suggest a danger in lingering too long, perhaps being trapped. I accept your proposal.

Also, it will be easier to only have to remember 4 names. ;)
You are short, and may at some point be mistaken for a Keebler cookie elf.

Your high dexterity means you are nimble and handy with silverware, though you may still be befuddled by the purpose of a spork.

Awakening slowly from the befuddlement that overtook his mind when he was somehow... transported here, Og'rialt is quick to take umbrage at these first words to penetrate his mind.

"Isn't that just always the way of things? Someone feels they're better, and so they issue commands! As a dwarf, trying to eke out an honest living away from my ancestral home, I've had more than my share of people feeling they're better than me, and it's shaped my very existence! 'Your majesty'" - and here Og'rialt manages to find the perfect middleground of tone where none could tell if these words were spoken with scorn or with respect - "I suggest you take stock of your surroundings and realize that at this very moment, you're no better off than anyone. Listen to the sound of those many clawed feet, and realize they mean bad news regardless of your station in life. Work together with respect for everyone, or see if the owners of those feet will be impressed by your title!"

"Strength in numbers is definitely something I find myself in favour of, but I'm not so certain that heading through a large tunnel is a wise idea, even with a large party. We already know there are many things with clawed feet living in here, and somehow I doubt that'll be the full extend of things. It might be my dwarven sensibilities feeling at home in small tunnels, but personally I'd rather encounter small monsters living in small tunnels, rather than large monsters living in large tunnels! And if those clawed feet were to gain on us, I'd rather face them in an easily defensible tunnel, particularly if we might give them a few surprises before they reach us!"

"Though we're here at the entrance of the large western tunnel, yonder small tunnels aren't that far away! I figure with the amount of time it's taking us to get organized, we might get just as far if we head south now."

Cardan, Half Orc Berserker, agrees. Cardan knows, many Half Orcs will get many shinies in dungeon! Cardan's 2-hand greataxe has +2 damage, very good, very strong. Crush enemies easy.
...Try not crush chests with shinies.

Cardan waits for others to join strong Half Orcs as well.

I am already heading towards the torch in the tunnel... I'd say let the chains to another group unless any of you have some kind of detection/inspection/find spell (mine are heal, cure disease, and turn undead).

Could you please verify if I get that right? This is a hypothetical formation of our party.

Hmm, another dwarf. Do you specialize in ranged or melee weapons? We seem to be lacking a ranged attacker but let me consult it with SmartyFartBlart first.

Kyp, a Dwarf Ranger ran here from the Northern Tunnel group and approached me, asking if he could join our forming party

What do you think? We do seem to be lacking a ranged attacker as of now so I vote yes.

I agree and we're already too far in the tunnel anyway.
The further we move away from that room, the better.

A note to my fellow magic users, by the way: I don't know if you sensed it too, but there's something wrong with the spells in this place. It's as if something is inhibiting mana regeneration.. we could be able to only cast a limited set of spells, so be careful friends.

Well, at this point we can't get picky, can't we? We shouldn't stay here too much longer, anyone else?

Also - Gold, any suggestion with way we should go?