The Shortcut
(2009)

When Taylor (Josh Emerson), Lisa (Shannon Marie Woodward) and Mark (Dave Franco) investigate the Old Man's (Raymond J. Barry) house, they find a chained man in the basement. Helping him escape, he turns on the group, killing Taylor and Mark with a sledgehammer.  Derek (Andrew Seeley) and Christy (Katrina Bowden) show up and try to help Lisa escape. Kristy gets seperated and killed by the chained man in front of Derek and Lisa.  The Old Man catches up with the three and shoots the chained man. 
 
The Old Man is Ivor, the older brother to Benjamin shown in the flashbacks.  His family realized early that Benjamin was a sociopath and had him chained to the property to prevent the secret ruin their family.  Ivor and his family had been covering for his brother and his need to kill for decades. Ivor tells Benjamin he's sorry but he won't kill for him anymore.  Benjamin dies, and Ivor commits suicide.
 
Just when it seems everything will be fine, Lisa is stabbed and killed by Tobey, Derek's younger brother.  He is a killer like Benjamin, and Derek like Ivor has been covering for him out of brotherly love.  They move Lisa's body so it can be blamed on Benjamin.  The ending dialogue suggests Tobey killed his father (and that is why the family moved in the first place). 

Thanks Spectre!