Demons are not “staff” in hell.
Satan and a portion of the angels rebelled against God. They were cast out of heaven.
At the end of time they will be put in hell.
People who reject God of their own free will (“The devil made me do it” is a comedy line, it does not impact the culpability for sin) are sent to hell when they die.
We do not know the specifics of hell. Yes, there are private revelations but those are not doctrinal beliefs. Scripture describes a place of weeping and wailing and gnashing of teeth and of utter darkness.
The greatest torture of hell will be eternal separation from God.
All of these pains of hell will be pains to the humans and the angels in hell.
The idea that Satan is the boss in hell and the demons work for him is simply a story.