Heyy. :) Sorry it took a while to get another response, first off. I highly disagree with the statements of the previous support leader, and if I were in your situation, I would too be extremely afraid about the mental status and situation I was in with my brother/sister. You have every right to worry, but you shouldn't let all of this consume you and hurt you (through stress, etc.) Sure you should try to seek help for him [if need be, you as well] but you shouldn't try to worry as much. Psychological disorders are extremely frightening, especially Schizophrenia which is one of the most bizarre and strange disorders to be found as of yet.
Luckily, some forms of Schizophrenia are treatable, and with the everyday evolving medical field, new treatments could come any day now. You've been around this your whole life, so it seems, and you deserve to be worried. You should, however, try to take a stand for it all. You know the situation, and since it sounds like no one is noticing it or acting on it, you should attempt to yourself. Tell someone about your brother, Tell someone about how frightened you are. Don't sit back and watch him get worse, because there is a point (most of the time) of no return. It's better to get him help before it's too late, trust me.
Honestly, there is nothing else that I can tell you other than getting him treatment. Schizophrenia is one of the oddities in psychology, and there generally isn't any other treatment I'd be comfortable with describing to you. Stay strong, stay calm, stay level-headed. I know you somewhat, and I do know you're smart, and that you will be able to get through this. Be cautious, aware, and ready to get him help. Tell your parents, tell someone who cares about you. Just don't bottle this inside and hide it, in a sense. :/ Good luck.
~Wayne