That fluctuations indicates the ghost just pass by you. Freezing temperature has to be constant in the ghost room.
There is a ghost that gives 4 evidences. One being obviously a fake one. The fake evidence is random each time.
To see ghost orbs, light in ghost room must be off. It's easier to see ghost orb in a small room but for larger rooms you must place camera near ghost's spawn point to see orbs.
No, they are secret cheat code that forces specific ghosts instead of randomly choosing them.