Yasmina reluctantly goes along with the plan but she mentions the risk of the archmage and his minions simply using powerful magic to take them all out if they stay close together. She would prefer if they all stayed back with better space to manuever and retreat and let Lord Amir take the enemy on but she knows most of the others are too eager to fight to even consider that option.

Yasmina's suggestion and observations give Delvindra significant pause.

"You're right. If we have enough time for you to summon Lord Amir again then he should absolutely be our first line of defense. I'd never considered the possibility of facing spells with larger effects, either. So, you think the larger chamber would be better because we can spend out? Or do you think we just need to find ways to keep our distance within the smaller chamber?"

"I suppose it would depend on what we're facing but we should expect arcane magic at least. A larger space gives more options but it is hard to say which site would be bet in the end." The red-haired Half-Elf says, looking around at the others. "I'm okay with what you were suggesting, I'm just saying there are risks with that too."

Cal will speak up, "I know it sounds very unwarrior-like but as long as we have these items, we are more of a liability than a boon to the people of this land. If even one item gets into the mad mage's hand then all could be lost. I believe we must leave while we still can."

So, to recap:

Milly and Delvindra were gung-ho about fighting the cultists in the burial chamber... until Yasmina suggested that in an enclosed space the party would be dangerously vulnerable to fireballs.

Cal wants to leave the island entirely and hope that the cultists pursue the party.

And we have not heard an opinion from Zander.

If it helps you decide at all, there are multiple burial chambers. The largest ones have enough space that a single fireball wouldn't engulf the entire room... but the tradeoff is that those chambers also have more mummies in them. Also... Lord Akkron has an item of power as well that Firion wants. It's likely that the cult will come to the island as well whether you're here or not. Though... perhaps you could persuade the lich that it would be in the island's best interests for him to leave as well until Firion has been defeated, but knowing what you do of Firion and the dragon cultists it isn't at all outside the realm of possibility that they might decide to bombard the Shaded Isle anyway out of pure spite when they realize that the lich isn't there to defend it.

Seeing everyone get quiet and look to him, as Zander has been sitting  back and taking it all in. “They are going to come. If we are lucky we have a chance to prepare, even luckier if we can pick the place. I’m ready for battle now, later, here or there. Strategy is for smarter folks than I. No plan survives first contact in a battle. “

"I'm not going to tell anyone what they should or shouldn't do. It's not the way of a proper Ilmateri," Delvindra lowers her eyes as she says it, "I've allowed myself to forget that."

As she raises her gaze, she looks at each of the Accursed in turn, Zander, Duwamilly, Yasmina, and finally Cal.

"As for me, I'm staying. Like it or not, this is where the fight is. A fight that we brought to Lord Akkron's doorstep. Whether Firion would have come anyway is irrelevant, he's coming now because of us."

"For those of us who stay, I think Yasmina's right. We need a place where we can't all be felled by a single attack. Because as long as some of the artifacts remain out of Firion's grasp, we still have hope. If it comes to it, I trust Duwamilly and Lord Amir to get us to safety but, if we'd rather have other options to escape, I'll go wherever you decide."

(To try and simplify for clarity. Delvindra would prefer one of the larger burial chambers to avoid all being hit with a single fireball and prevent being attacked from multiple directions, but will go wherever the group decides; only asserting herself if she needs to break a tie vote.)

"Nothing against choosing a large burial chamber, kids!" Duwamilly agrees, optimistically, rearranging a stray lock of honey-colored hair as she speaks "After all, this way, if we manage to reposition the mummies in the access corridor... there will be more of them to defend it!"

The red-haired Half-Elf smiles and nods in agreement with Delvindra, ready to prepare to meet Firion and his forces.

"You are right Delvindra, the fight is here and we must deal with it to protect those who can not protect themselves. Let's go to the dead."

So, with the decision made, you continue deeper into the catacombs. The tunnels twist and turn, and they are nearly pitch black (I think all your characters have darkvision, though). These ancient caverns are disturbingly silent. Not even the sounds of bats or other wildlife reach your ears, as your own footfalls echo through the seemingly endless tunnels.

Eventually, after what feels like an entire day (and, admittedly, it was likely at least an hour), the spirit brings you to a huge doorway. Unlike the rest of the cavern, there is an eerie light illuminating doorway, though you aren't quite sure what the source is:



On the other side of the door, you can see the inhabitants... 15 ancient corpses, propped up into sitting positions. The dead sit silently, seemingly unconcerned with your presence.

Duwamilly is waving already and about to greet the ancient corpses... but she stops, suddenly remembering that not all undead are as welcoming and benevolent as Lord Matic Akkron - and that the lich gave the Accursed a magic item to avoid them getting noticed by the 'inhabitants' of the catacombs. So maybe it's better not to draw their attention, at the cost of being a bit less chatty and less polite than usual.

"Well, kids..." the ex-Preceptor's brown eyes run from the corridor to the chamber "Maybe we should start by trapping the corridor? Finding good places to weaken, so that it will be easy for us to make the ceiling collapse on the invaders' heads?"

"After that," the gnome cleric goes on "we could slowly relocate the... 'inhabitants'... to the corridor (not under the trapped parts, of course) so that invaders will be forced to disturb them - and face their wrath. If the strongests among us can move the seats of the undead gently, maybe the undead will not notice or at least not care, because of the protection Lord Akkron gave us".

Delvindra digs through her pack and returns to her fellow Accursed. She hands Zander and Cal each a vial of red fluid.

"Potions of Healing. In case you get hurt and Duwamilly can't get to you."

Next, she hands Duwamilly a scroll.

"Dispel Magic. I don't know if it will come in handy here, but I'm sure you'll find a use for it," she hesitates a moment before releasing the scroll, as if there's more that she wants to say, but settles on a small nod before moving on.

To Yasmina, she offers a vial of bubbling blue liquid and a parcel wrapped in brown paper, "a Potion of Heroism and..." The words catch in her throat. "... they're so beautiful. It would be a shame if anything happened to them... and I won't be needing them anymore."

"... when I go back to the monastery," she adds without making eye contact.

"Delvindra, honey..." Duwamilly is perplexed "What do you think you're doing? Sharing your things as if you are going to die... Wrong! Point one, we are here to win (or at worst to flee after having given Lord Akkron an advantage), not to die. Point two, we divided the scroll to maximum the chances one of us is able to contrast magic, if needed, so keep your one... I also have one. Ii will be safer that way".

"Thank you Delvindra. Hopefully we won't need it. But its good to have."

Zander adds it to his pack. 

Yasmina follows along, ready to seek out a good position for herself in the expected battle, feeling quite uneasy with the collection of corpses lining the walls. As the Tiefling offers her  the potion and the parcel, she accepts the parcel, curiously opening it. "You keep that potion, not that I don't think you are heroic enough, but you would need it's effects more than I. Also, I don't want to sound pessimistic of our chances here but maybe I wouldn't plan much what I would do after all this. I mean if it helps you going if you think about how much you want to return to your precious monestary then by all means, but just maybe you will make another decision if we get through this together." The red-haired Half-Elf says a bit cryptically as she opens up the parcel and looks inside.

"I know it's not your size, but you should be able to get it altered easily enough," Delvindra says as Yasmina opens the package to reveal the silk robes that she purchased on their shopping trip, the ones that she exchanged for warmer clothing when they made the journey to the dragon's lair.

"And I have no intentions of dying," she says to Duwamilly almost convincingly, "but it doesn't make any sense for me to keep all of these things to myself when the rest of you might need them."

"Besides," she tucks the scroll back into her pack and pulls out a vial of syrupy, iron-colored liquid, "I still have my potion of invulnerability."

Turning back to the Half-Elf, she offers the Potion of Heroism one more time. "Don't be stubborn. If you don't take it, I'm just going to give it to someone else."

"While I'm thinking about it, I also have some darts," she says to Zander and Cal, "in case either of you need a ranged weapon. I have my short bow."

I do better up close 

Here's a basic map of the area:



As you can see, the chamber itself is 80 ft across, and the tunnel leading into it is another 20ft wide. Behind a coffin (and, by extension, a mummy) at the back of the room is a small doorway that presumably leads into a secondary chamber.

How do you plan to transport the mummies and/or booby trap the hallway to give Firion and his cultists a warm welcome?