Eh. These people were garbage but I don't think the story is saying they deserved to die. It's very obvious the murders destroyed Sora's mental health and not what he actually wanted, which is just for Hinata to save him and spend is life with him.
Which he can't do the moment he falls to the dark side (as he said himself) hence he's basically spiraling and acting "nonsensical" ever since, since he doesn't see a way out.
While the story doesn't say it, it's not condoned in any way and even the characters just "don't care that much". Hinata says it wasn't his fault for this, and his parents barely get any more developpement than just being pieces of trash so they're not even humanized. And while killing them definitly isn't the right option for the victim, i think they deserve it
Sora's parents and the teacher absolutly deserved to die like this, but not shinohara, and i find it so beautiful and tragic that Hinata is willing to forgive Sora if he lives an honest life despite all of this (and how he doesn't go like "oh but you shouldn't have killed them they're human !!!" Talking about the 3 first murders)