Could be The Aggression Scale (2012).
The following are snippets from reviews. First, we meet the ''bad guys'':
Someone has stolen money from a mob boss, and he wants it back. He
hands off a list of suspects to his number one henchman with a simple
order: kill every person on this list until you get to the embezzler,
get the money back and kill him too.
Meanwhile, we're introduced to the family:
Newlyweds Bill and Maggie move to the country to start a new life.
They are joined by Bill’s son Owen and Maggie’s daughter, Lauren. It
seems, however, that the family left some loose ends behind in the
This segment talks a bit about Owen (pretty much how you described him!):
The syndicate boss, Mr. Bellavance, sends a group of his men to the
family’s home to teach them a lesson. However, he was not counting
on Owen. Recently sprung from a juvie mental hospital, Owen has some
issues, including a penchant for spectacular violence.
You can watch a trailer here.
~ Synopsis edited from ShockTillYouDrop and BadassDigest