The parents now look like assholes for lying about their children. The intention may have been nice, to not "set expectations", but that just led to a lot of pain for the friends of their children involved. As they say, the road to hell is paved with good intentions.
Michi's mother in particular is a nasty one, for emotionally scarring Chiaki like that when she was still a child. She didn't have to do it that way, but I guess she just wanted to lash out at somebody, even a child.
I understand that some are frustrated that this didn't really turn out to be a "murder" mystery. This wasn't so bad for me though.
Two things hinted at it for me:
1) When Kenta violently wrecked the "memorial" to Sahara on the ground in one of the early chapters. He mentioned it again this chapter. There's no reason to do that unless he either hated Sahara or thought it was an insult to a friend who's still alive. I knew that had to mean something.
2) Sahara turned out to be an
unreliable narrator as you point out. This is a writing technique I don't see often, but could backfire badly if not handled well. Much of the early things in this manga was from his POV, but when he started having flashbacks inconsistent with what we saw at first, that was when I realized it and stopped trusting what we saw from his POV.