Parents trying to off my brother

My brother (22) is still living at home. Youngest, of four, only boy. He's unable to hold down a job, has dropped out of college, is currently in a technical school (all funded by parents, of course) he has not one but two rooms in my parents house. Parents pay for everything. (They pay him to do things like mow the yard, I think something like $70, and last time I talked to my mom she said she was doing it) Since highschool he's struggled with depression how serious I don't know, as my parents are super religious and mental health issues are really just chalked up to a lack of faith. He has also been known to abuse alcohol and drugs. This year, my parents bought my brother a motorcycle. In my opinion they could have just bought him a loaded you know what and pointed it to his head. My question is: can they be held legally responsible when he gets seriously injured or unalived, or when this happens to someone else because of him? This 22 year old is unemployed and would have never been able to afford a motorcycle until his frontal lobe was fully developed which is what I was really counting on and my parents decided to buy him one. He would have no means to have done this on his own. I love my brother and I'm honestly not shocked at my parents choice, they disappoint me more and more the older I get, but I'm just wondering if anything can be done when the worst inevitably happens.