So I'm clear, we have a tunnel with an unknown other end that our guide Cydney is running down?
If that is the case, then I think we have a new best option.
Benlin can make a Permanent Illusion of us debating what to do and we all move down the tunnel. (thoughts before he actually does that)
Wake flies after Cydney. He is an umber hulk, but he has Overland Flight on him. He is in the telepathic bond by virtue of Benlin have cast the spell so he gets to share it. As with the other spells he shares, because of the feat the extend beyond five feet. He has a 12 Int and a 14 Wis, so he is smart enough to do this and stay in the bond.
He also has the Luminous Armor so, the area is lit up for Cydney and him. He flies at 45 (40 +Elation 5), and can double that with hustling, so he Shuld be able to keep up with her.