I don't think they've ever done a single thing except get people killed.
They're responsible for some of the strongest gun control legislation currently enabled in America today. What the fuck do you mean you "don't think they've ever done a single thing"?
Stadia was a Squandered Opportunities masterclass. That platform had SO much potential; the tech was there, and the tech worked, but Google hired the worst possible person to run the project.
He is unstable and dangerous. Killing animals is a universal first indicator of future violence against people. Don't take his threats lightly, even if you parents seem to do so.
If you don't want to call the cops on him (which, IMO, you definitely should), then you should be prepared for the worst. And by that, I mean arm and steel yourself for the worst case scenario. There is a non-zero chance that he'll put you in an it's-you-or-him situation.
It won't be your fault if he puts you in a situation where you have to put a permanent end to his threats. It'll be hard to live with, but you'll still live. Which is why I recommend letting the police deal with him, instead.
It's hard when it's family, when it's somebody you grew up with and still have love for. He's broken, and it's not your fault he's the way he is. Nobody can help everybody, but you can still help yourself.
Good would still be alive if he had.