I don't get how these kids always seems down with murder. I can see them being selfish, bullying, wanting to attain higher status and all that. However to actually plot with your mom to kill a person who has done you no wrong without any reservations? Talk about some seriously warped parenting.
Also lets not forget what a scum bag the dad is. Not only is he hiding the fact he had a secret love affair that produced a child, but then he has the audacity to invite them to live in the house of his wife under the guise of charity so he can carry on an affair. In my mind he's also holds some blame for his wife's death as they wouldn't bother to kill her if they didn't already have an in with him to take over the household.