Oh, my!!!! I am SO SO SO SORRY your son and your family are going through this! That's so scary! I would be afraid, too. Sometimes kids do kill - although more often than not, they're all talk, no action (whew!). The fact that he's saying this sort of thing - that's enough reason to take it seriously. Better to be safe than sorry.
It's true, it could be the parents' fault - or they might have a hand in this boy's behaviour. But as you can see, they might have been doing all they can.
Gosh, I really hope this all turns out well for you! I'm invested now! Would you please PLEASE keep me posted about how things are going? I'm concerned about your son feeling bullied and afraid at school, and your family being worried at home. Just want to know everyone is okay, and hopefully get some good news about this troubled boy receiving help.
Sending you love and hugs, too, and yours are gratefully received! 💜