Well, I mean, he should get an appointment not just to prevent him from harming himself or others, but simply to have a better quality of life. I'm sure he's not living life to the fullest with the disability holding him back.
He won't get locked up- if you're in the US, you can't hold someone against their will unless someone is in immediate danger. Just being schizophrenic and untreated is not reason enough to hold someone.
Unfortunately, a person who has schizophrenia needs constant maintenance and communication with his doctor to adjust medication as needed- throughout his life. It's not a one-time fix.
Hopefully your parents will come around- all I can say is keep bugging them- not just for your peace of mind, but to help your brother out. He doesn't seem to have much of an advocate right now. He needs someone who is concerned about his well being.