(For sake of updating, I'm assuming the group does send Jack and Shadowlyn ahead.)
The two halflings scout ahead, and after some time they peek into a big hall, tall enough for a human to stand normally (I'll drop some charges from that reduce person wand at the end). It's propably 70 to 80 feet long on each side, and at the far end, you can see another tunnel leaving to the north-east. A large portion of the room is taken up by a column of red light. It is certainly the curtain of light from the temple, and thus you seem to have found the area to cleanse. The construction workers will break through in this place after you sealed it.
The column is a bit south of the center of the room, and partially vanishes into the south-east wall. Around the light, a number of skeletal rats stand, sometimes making a move towards the light, but then quickly jolt back. Three of the fungus creatures also stand around the light, one of them clearly the "winged" creature Lothé described. It and another one of the fungus creatures seem a bit darker in color then the fungi you encountered earlier.
As you watch, the winged fungus shoves one of the skeletal rats into the light. The skeleton quickly jumps back, though it seems unharmed. The light seems to have dimmed a bit in the process.