Point of the story is the Hero blackening into a villain for revenge. Don't think the twins could be redeemed. They were raised in a twisted environment to be sociopaths. Their gleeful torture and murder of animals and implied humans demonstrated their already degenerate characters. Children ccan be just as dark and twisted as adults. There are a shocking number of murders committed by young children from normal upbringings. These are not children that could be trusted in society. At best they would be institutionalized.
Then, explain to me about what if kids who are under 15 years old that killed lots people, but released shortly because they are kids/underage but after the released, was caught again for killing more? You still think because they are kids they shall be forgiven? I say better kill them for the sake of other.
What if you are a judge, and you released a kid who killed his younger sibling, then that kid who got released, killed his neighbors little friends as well? If that will be the case, I believe your name would be in the 'People MC Gonna Kill' Lists.
I not saying he should let them go free unpunished, but kept as a slave, or something teach them right from wrong, give some form of punishment befitting for them at the same time rehabilitation. But I see you're point, it'll be too much hassle, we should start killing child-soldiers, children of ISIS and other terrorist groups, cartels, and so on. F**k the civilized route. I'm guessed l'm just wired that way to be protective of kids.
I wish there was an interdimensional police can arrest this asshole!!