Out-of-game communication.

Dear GMs, please explain these blunders to me, a simpleton:
1. How could undead fall for an illusion trick? They are dead; they cannot be fooled by such things; they have immunity to mind-control spells.
2. How can Adu be thrown into a dungeon? She is a ghost; she cannot fall; she floats.
3. Will the demons just mindlessly fight the undead without trying to understand what's going on? Are they complete idiots? And Tengro, who was there at the time, didn't suspect anything?
P.S. IMHO.