(Sorry for the double post.)
I feel the title is a little bit at odds with your logline ? Beverly Killbillies? sounds like a dark comedy, maybe grindhouse, but the logline is definitely not comedic. Deliverance meets I Spit on Your Grave. I'd totally watch this.
Inbreeds? is a verb, so maybe inbreds? is more appropriate? Homestead? tripped me up too ? brought to mind visions of farming? Thoughts of children being terrorized and slaughtered gives me the ickies. Is the protag really a child or more of a teenager?
Appalachian inbreds break into a Beverly Hills mansion, terrorizing and slaughtering the family one by one, until one of the children escapes and gives the killers a taste of their own medicine.
or
When Appalachian inbreds break into his Beverly Hills home and terrorizes his family, the eldest son/daughter escapes and turns the tables on the home invaders.