What was the deal with the mannequin?

So the guys come across the lair of the underground cannibal dwellers because they are attracted to the sound of a television. Within the lair, there is what appears to be a type of trailer and inside is what appears to be a woman watching tv. The "woman" turns out to be a mannequin dressed in a woman's dress and wig. Later in the film, when the final two survivors are captured by the cannibals, they dress the female up in the same clothes and prop her in front of the tv. Who is the mannequin supposed to be? Is that supposed to reprsent their mother? What was the point of it? None of that was explained. If they needed a human female to replace the mannequin, why not use the first girl they killed? Meanwhile the surviving male is chained upside down. What for? Why not just kill him then and there? No one else got such consideration. Why were these two spared?

Anybody figure any of that out?