I know this is way out in left field, but that never stops me from embarrassing myself by sharing my thoughts. What if the guy wasn't planning any of what happened to begin with. Is it possible that someone on some heavy drugs (or alcohol) was going through the vehicles looking for something to steal and found a hunting rifle or shotgun in the truck. Mollie starts barking and growling because she hears him out there, and Dad goes to check it out. The guy is close to the house at the time, and even after turning on the exterior light, Dad doesn't see him. Thinking there's a bear, raccoon or something out there, Dad opens the door and shoots in the air to scare it off. That startles the thief who was fairly close to the door and wasn't thinking clearly, so he opens the screen door and shoots through it to retaliate. He hears Dad fall to the floor and forces the door open. When he does that, he hears DC scream and sees her run into the other room. He goes after her and shoots her too. He wanders around looking for things in the house to steal, but JC comes out of her bedroom to see what woke her up. He's trying to shut her up because she's too small for him to consider her a threat. DC calls 911 but dies before she can say anything. He grabs JC and she yells for help as he's dragging her toward the front door (or her bedroom, whatever) and passes DC's body on the way. He notices the phone and hears the 911 operator asking if anyone is there. He kicks the phone and drags or carries JC with him to get out of there before they send LE to the house. He would also have been likely to grab whatever Dad had shot out the door too since it would be something he'd be able to sell.
It may be less than believable, but you have to admit it's original. MOO