I'm baffled as to why the mother demanded Hanks open the door and save the man who's kicking them out of their home.
If he dies, the children will stop killing and the family will own their home. Also, he's clearly a jerk !!
Why on EARTH would she demand they try to save him ?! Come ON ! His death solves EVERYTHING !!
Not letting a person be hacked to death by zombie children and then eaten is sort of the human thing to do. In other words, it was out of compassion. Also, it's a point in the story to show that Carlton is a bad guy (such as when he pushes the older daughter out of the way so he can escape first) and that the mother was a good person. They wanted to make the lines between good and evil more visible by throwing it in your face how really bad he was, and how really good she was. While I don't agree in letting someone die, I do understand why some others would let it happen.
It was a pointless thing to add though. He was a massive jerk. A little too much though. I think they overplayed it a bit.
Further, him dying does not necessarily solve all their problems. We can see this because he does die and their problems are not solved. Carlton states that the zombie kids are bestial and that they will go after anyone, even the ones they normally don't go after (such as blood relatives) if they get riled up enough. So letting him die at the door isn't necessarily going to save them.
The zombie children are still haunting the woods and will continue to waylay unsuspecting people and eat them. *correction* I might be wrong about that. Maybe they will stop killing because Carlton is dead, but that really makes no sense. If they wanted to kill off the bloodline, why were they eating every other idiot that stumbled their way?
Yes, he owns all the land and everything on it, but him dying doesn't mean everyone owns their homes. More likely his estate would be passed down to the next of kin and if there is no next of kin it would probably be given to the state and who knows what they will do with it. If your landlord drops dead, you don't get to live in their apartment rent free, do you?
In any case, at the end, the older daughter and the mother are discussing what they are going to do now that they have left and it is mentioned that they did not sell the place like they intended. They just packed up and left. Wise choice, in my opinion.