Ugh. Why couldn't this be more simple? Two "pretty", "role-model-esque" kids, but a nutty guy defending his property and taking it too far.
I think I was fine with what I read until the part of repeated shots to the chest and a finishing shot under the chin. I further doubt someone laughed at a guy after being shot and falling down the stairs. Unless they're trained for that sort of thing, I'd assume 99.9% of people would be scared shitless in that situation.
Long story short, had it been two shots, two kills, and a prompt reporting to the police, I'd say this would look much, much better.
As it's reported, it sounds like murder, or manslaughter at the very least. A man has a right to protect his domain, but taking the time to find another weapon and finishing shooting the burglar seems to be above and beyond. Get out of the house, call the police, and have them handle it.
Shooting them is justified, finishing them off when likely out of harms way is completely over the top.