(Sorry Rodolfo, will have to retcon your post, Skameros posted first.  You can recover your spell slot.)

Skameros DC 13 Dexterity Saving Throw: 10

Group insight check (skameros is busy looking elsewhere):

• Beegred: 16
• Rodolfo: 23
• Grithik: 17

Edit: Actually, Skameros has advantage on DEX saving throws...  roll: 9

Skameros walks forward 5 feet, looking at the floor the gnomes are pointing at.  The armored gnome uncrosses his arms and starts to wave his hands, miming 'stop' but it is too late.  As Skameros moves forward another 5 feet, the floor he steps on tears under his feet and he falls through the material into a spiked pit.

Skameros takes 6 blugdeoning damage from the fall, 4 piercing damage from the spikes, which are stained with some kind of substance.

Skameros DC 13 CON saving throw: suffer 17 poison damage on a fail, none on a save.

Rodolfo and Grithik notice the armored gnome slaps a hand to his head, apparently distraught at this outcome.

The gnome kneels down at the edge of the pit and extends a hand towards Skameros, beckoning him to take it.

Edit to make the dice roll!

Edit #2: forgot Skamero's Con Save!   Saving throw: 24

A pained yowl comes from the hole in the floor as Skameros gets skewered.

He then climbs back out of the hole and glares angrily at the gnome

"Dirt nome should speak instead of wave arms around.  Or are you where rat?  Now Skameros angry.  Not good way to start talking.."

As Skameros refuses the gnomes outheld hand and begins to climb out, the pair of disheveled gnomes back off, make eye contact with the others, tilt their head to the east and disappear eastward around the corner before Skameros finishes climbing out.

Now that the trap has been compromised and Skameros has torn down the cover in his attempt to climb out, the group can see a 15 foot by 15 foot pit, 10 feet deep, lined with zurkwood spikes, their tips stained dark with some substance.  On the eastern side of the pit, there's a 2 foot lip along the cave wall that could have been used to avoid falling in.

Once Skameros climbs out of the northern side of the pit, he sees a narrow passage heading eastward.  To the north he can see another large cavern that splits in two directions, north-east and north-west.  Looking at the narrow east passage, he briefly sees movement as the pair of gnomes disappear out of his sight.

(The party can choose to climb down into the pit, cross and climb out.  The only potential danger for doing so would be coming in contact with the substance coating the spikes.  The alternative is to make a DEX check to shim along the 2 foot lip without falling uncontrolled into the pit)

Skameros will unwind some rope from around his waist and toss one end of it back across the pit so that the others can traverse potentially safer.

Rodolfo grumbles to himself, "********. Are they mutes or something? He kept pointing there and then looked surprised or even remorseful when things happened."

He calls out, "Skameros, you're OK?"

Is there anything on this side of the pit to tie the rope to?

Beegred will hold the other end of the rope.

After both spell-casters are across, he will slide across, still holding the rope. (Hopefully, if he is about to fall, Skameros can tug the rope to get the halfling the rest of the way.)

DEX save (without advantage):

Rodolfo hands the end of the rope to Beegred, "Thank you." and will move across on the side. Dex check: 10

"Certainly a nice trap, at least..." Grithik admires as he makes his way across the side using the provided rope support.

Dex Check: 17

After crossing the pit and stowing Skameros's rope, the rest of the party can see eastward where the gnomes went, a narrowing corridor that appears thick with spider webs further in.  To the north, a large cavern leads north-east and north-west.

Skameros heads after the gnomes

The passage here narrows where only two can walk side by side.  This passage seems rarely used as it has an abundance of spider webbing the deeper you proceed, until a sheet of webbing seems to cover the whole passage, blocking your way.  There are a few gaps in the web where the smaller folk could reliably step through, but Skameros would be hard pressed to get through without widening the gap further. 

As you approach this sheet of spider webbing, the gnomes step out approximately 10 feet on the other side of the webbing.  They point to the webbing, shake their heads 'no' and cross their arms, waiting to see what you will do.

Rodolfo says quietly (in common), "Lets back off a bit, this is another trap. Actually, lets back off more than a bit, I'd like to see if I can set this webbing on fire and clear us a path both forth and back. I have a hairy feeling we might need to get out of here in a hurry."

(if everyone agrees then he'll use prestidigitation to try to ignite some webbing. If it doesn't work then he'll light a torch instead and throw it further forward)

"They certainly seem to be honest, so far. Not to mention I'd prefer to stay out of spider's webs as a general matter of habit." Grithik listens to Rodolofo's plan, "I have something that I can try as well. The torch idea makes me nervous."

(Grithik would try a Sacred Flame if Rodolfo's initial idea doesn't work)

When the two gnomes realize that you are attempting to burn the webbing, they run and throw themselves to the ground around the corner, where you can't see.  Rather quickly, the spells burn a tripwire that was camouflaged in the web and a massive pile of stone falls from the ceiling just beyond the remnants of the web, where the gnomes were standing a moment before.  Dust billows into the passage, obscuring vision for a minute or so, as the dust settles.

(is the passage blocked or is it just a layer of rubble on the floor?)

Beegred had his sword out, and was about to chop at the webs. After seeing the fire trigger the rockfall, he whistles a simple tune, discretely puts away the sword, and takes a few steps back.

Rodolfo says, "After you, Skameros. Be careful though." 

"Went better than the first trap, at least..." Grithik muses.

Skameros leads the party through the passage, past where the spider webs were, to stand on the rubble of the trap.  The two gnomes are once again out of sight.  Entering into this cavern reveals the source of the rotten stench noticed earlier when entering the wererat warrens.  In front of your party is a huge mound of rotting garbage, composed of all kinds of decomposing matter, including a pair of slimy, partially digested svirfneblin corpses.

(The corpses appear to have been there for many days, so you don't confuse the corpses with the two you were following.)