I'm breaching hell now, wish me luck...
EDIT: The sacrifice has broken the seal. The spikes are ready. Blood shall flow.
WHAT? THEY'RE NOT GOING FOR THE SPIRE? RETRY
EDIT2: Okay, doing this again. Working much better, the sacrifice and the humans lured them into the trap, 15 died before they got away. Many more demons are injured. I wish I had put the cages separately so I could release one human at a time. Also, a crossbowman managed to make it out the edge of the underworld, wow.