They stand outside the Hall of the Dead, guarding it from intruders. Nothing is known about them aside from being guards that are extremely loyal to Set and their city.
The other sentry is a glowing one, in front of the entrance to Vault 12, and will become hostile towards anyone trying to enter. If they turn hostile, other ghouls, including the glowing ones inside Vault 12 or above, including Set, won't become hostile.
If the player character talks to them while trying to enter the Hall of the Dead, they will tell them to go away and that they don't want their kind around there. Despite the warning, the Vault Dweller can run past them without any repercussions.