Sounds like sociopaths all around here.
He shot the kids, wounding them and then shot them again after they were down. Guy's an obvious nutcase and cold blooded. If he had shot each of them once, taking them down and then called the police, he'd be okay. But he stepped way over the line. Can't sympathize with him.
However, that girl laughing after he shot her once. Either she reacted that way because she was in some kind of shock or whatnot or the girl was also a sociopath.
Since the kids broke into someone's house, I can't sympathize with them. You break into someone's home, you get exactly what you deserve. However, can't feel sorry for the old man due to his cold-blooded nature.
Everyone's at fault here.