Day 1

As you move into the maze through the doors it appears as a labyrinth. Sunlight from the outside disappear after a few corners. Walls come closer- corridor is only few feet wide and you have to squeeze.
You hear seldom cracks and ground vibrating - this is what the other mare runners described you previously usual for this place, you don't hear any voices, screams or whispers that they warned you of.

Yes have darkvision for 1 hour. So Bellow goes first. Who next and at what distance (5ft or more) ?

OK, so your moving order is: Bellow, Phoenix, Anguis, Elrond. As you move you feel sick because it smells of rotting and dead. But you have no choice but to continue.
After a few minutes walking path leads remarkably downward. With his superior darkvision Bellow spot a larger cave (something like this)
However while looking for details there [ ooc] and because in the dark you have -5 penalty to your passive perception[/ooc] when you step on just another stone it turns out to be skill and it breaks under your weight.
Bellow: you must to dexterity saving throw (you do it with advantage as barbarian because you could see. DC 10 (or you will fall and roll down).

You all hear skull cracks and Bellow start falling but he swings his two hand axes into the walls and stops, hanging. You hear Bellow heavy breath and you hear ... Grumbling, Snarling, Hissing from the caveIn any case, you continue slowly and carefully until bellow could see the whole cave. He see a humanoid form on the other side of the cave, but as you only see shared of grey you can't really understand what it is. I've marked green bubbles for you and red for the creature you see.

Bellow - you step over other skills and and over some rotten flesh... there is a mess of dead bodies both humanoids and beasts. You make some noise stepping on the bones, but they don't seem to be loud enough for the creature to pay attention.

Elrond, the smell around you and the sound complete the puzzle in your mind - you are certain that the creature you see is a ZOMBIE!

OK, everyone roll initiative. French - you will need to repeat your actions in initiative, but you will get surprise round.