Margret says to Nobody unparticular "But, How are we going to get one to him with all the webs around? And there is a phase spider out there. That killed his mule" she starts hoping that Gundren went to town 

You return to the workshop (putting up a watch or baricade?) to rest and split the items between each other to study them.

Otrov, there is only a very thin layer of green dust on the corpse, not enough to be usfull as poison but if you want to collect a sample and cultivate your own mushroom colony, you can add a spore sample to your inventory. 

Anyone going with Otrov to check on the spider corpse? (Kai would join you.)

Zurzg gives Margaret a funny look. While not the brightest gem in the mine, he could've sworn the way was fairly clear leading back to the entrance after their chasing of the Drow. But then he just shrugs, says nothing, and follows after Otrov hoping to at least score some chew spider innards and maybe collect some weapons from the bugbear bodies. Maybe even some javelins if they had any too! Oh, and maybe McGoblin some spider parts together into makeshift weapons.

Again not knowing the conditions of the way back, and even a little put off at the idea of facing a Phase Spider of all creatures, he simply bowed his head and accepted the woman's judgement on the matter.

Does Nobody know what a Phase Spider is?: 20.
(+3 instead of Nature)

Now when Otrov broached the subject of skinning the shapeshifters for some macabre but... maybe useful purposes, the tiefling grimaced before using the excuse of needing the break too much to be of any help any time soon.

When the short rest is over he asks, "So, what is the plan now? Do we head back? Or, are we to check out that building to the south before we go? Could have more clues on what exactly that Drow had hoped to accomplish, or.. even another figurine inside to use on the dibbly do." He gestures over to the magical fountain of power.

(I think you mean Zurzg)

(I did. I noticed this before I posted it the first time. But apparently, I got so sidetracked by other edits after that I forgot to go back and fix the first error. lol.)

Margret looks at Otrov while doffing her armor and putting it in the green flame "I really don't think its wise my friend. Just cause we chased off that Nezmar doesn't mean there's not more danger lurking. We're going to have to finish this place together but , we need to find Gundren If he comes here he might run into the slime" she goes over after doing so and starts to try on the breastplate for size if no one objects

If Otrov goes off she says "Don't be long be safe" she refreshes the pitons light or gives her a new piton with the light spell on it. 

light

„I‘ll go with him, the furnace is not far from here and at the smallest sight of trouble we come back.“ Kai says.

Otrov

She bathed the spectators eye in the strange flame and, to her delight, it comes out glowing!  Better still, the flames seem to have hardened the outside a bit so it’s not dripping goo and eye juice everywhere.  The halfling and Kai walk back to the corpses, being careful and quiet, with Otrov holding up the eye for light. After a scare, Otrov puts the poison in the vials and smiles. Won’t last long, she thinks, but better than nothing. Back at camp, she collects some of the spores off the bugbear, in the hopes that she can grow some of these interesting mushrooms in a small colony. 

Dain would be resting and studying the magical items the group found so far. Not much else he would be doing during the short rest.

She also tries talon in the flame maybe she can feel the difference being attuned to it

HD12

I will assume that Dain helps you with examining the sword.

The Mithral Longsword behaves unlike the other metal objects: it seams to resonate with the magical flame. It absorbs the magic much faster, as if the energy gets funnelled directly from the pommel, through the inlayed decorativ elements into the blade. It seams capeable to absorb much more energy then any of the other objects. But once you take it out, the energy flows out of the blade (the pommel to be precise) with a breathtaking speed and no matter how much you try it wont hold the enchantment for longer then a minute. 

"Seems like you need something on the hilt to keep the magic from flowing back out." Dain says with a nod to the mithral blade.

 She nods to Dain "Do we still have the Sapphire? Or any gem, I'd like to try it."

(Does Dain have some gem? I don't believe he took one anywhere along this, so maybe someone else has it?)

Nobody dozes off completely partway through the break. Although he started to get curious with the ongoing experimentation, without any threats to worry about, sleep deprivation had finally gotten the best of him.

(To DM: I don't know if you want a survival roll to see how much spider part rations Zurzg is able to put together, but here's a roll just incase: 20.)

Let‘s say he can break of as many legs as he wishes, 4legs =1 dinner once cooked. (I don‘t know enough about spiders, so i assume they work like crabs)

So equipment:

• Dain keeps the Staff, the gauntlets and the mace
• Margaret the armour
• Otrov the spider venom, the spores sample and the wand
• Nobody his skin

You keep on exploring the cave, hunting down the slime, taking a long rest somewhere, return to Phandelin what is your next step?

Dain would want to check out that unexplored building once the rest is over.

Happy with the Breastplate "I think its best we leave this place and tell Gundren our progress. Head back to Phandelin and get some real rest guys. We can get to the last rooms tomorrow. We need our tiethling at full strength. Besides we need info so lets take the head of one of the bugbears"

She gestures to the pile of half plate armor  "Someone going to wear the armor? I guess we can sell it for a few gems"

she smiles

"Of course we'll be honest about the magic to a point. We don't want snoopers here."