A married couple (who were also revealed to be biological brother and sister) who were never named beyond "Mom" and "Dad" the Robesons were brutal landlords who were prone to evicting the poor black people that lived in their dwellings, which were more akin to ghettoes than true housing - the Robesons were quite open in their racism towards the black race and as such were unlikeable almost from the start.
However their true colors were revealed after one of the boys from the ghetto sneaked into their home and found himself ensnared in a terrible struggle for survival against what he believed at first to be monsters known as the "People Under The Stairs".
The terrible truth was soon revealed to him, the monsters were actually the horribly scarred sons of "Mom" and "Dad" who had been locked up and abused terribly by the Robesons and kept hidden from the world, the only child that was spared this fate was their sole daughter named Alice, though even she sought a means to escape the horrors of this twisted "family" - the boy decides to risk his own life to try and rescue the other children as well as himself.
In the process he gets into a confrontation with "Mom" and "Dad" - after a few failed attempts at alerting the authorities of what was occuring the boy (named Fool) once again braved the house to try and rescue the children himself, which he ultimately succeeded in doing and they ganged up on "Mom" and killed her.
However in a particularly memorable (and terrifying) scene "Dad" arrives welding a shotgun and dressed in full BDSM gear, the madman goes into a frenzy and chases Fool across the house before he is defeated when Fool sets a room of explosives on fire.
As Fool and the children escape the explosion all the ill-gotten money "Mom" and "Dad" had hidden in their home started to rain down and was collected by the tenants as Fool helps the children to escape into the night..