Don't think schizophrenia shows in brain imaging, nor is the behavior you're describing match that diagnosis. On this forum there are no experts in mental illness, just folks who live with it. It's hard to diagnose mental illness in very young people like your brother -- the problems young people have don't necessarily translate to the chronic mental illnesses adults get, which usually, though not always, manifest in late teens until late twenties. You're not responsible for this behavior unless there's something much more dramatic than just not being the best brother you could have been. When we're young, we're often not the greatest of siblings, but you have a lot of life left to make up for it. There's no way for us to know if this is some severe mental illness coming out now or something happened that he hasn't told you yet that shook him up badly. A good pediatric therapist can often bring this kind of thing out of kids, though it's not easy as kids of that age have incredibly vivid imaginations. This is a job for your parents and the doctors and the psychologists, not for you. Your job is to be as loving and supportive as you can be and maybe you can also see if he'll tell you about something he saw or experienced that brought this out. Also, saying he's always suffered from anxiety isn't necessarily true either -- again, the very young often have fears and nightmares and phobias but they also often go away when they get older, so it's just too soon in his life to know this. Some kids are rash, some are bold, some are timid, they come in all shapes and sizes and personalities, but you know more when they become adults. Maybe a friend of his is dying, who knows? Again, there are psychologists who specialize in treating children, so here's hoping either the docs figure out a physiological cause or the therapists find a fix. This post shows your true self, which has been playing at being the big bad older brother (I had one of those) but deep down you obviously care a lot about the little guy. All the best.
I'm sorry to hear about your brother. He sounds like he is in emotional crisis. I think your parents need to expedite or speed up their asking professionals for help. Where I live, the alarming statements of wanting to kill himself or others and change in behavior (biting) would warrant a trip to the children's hospital emergency room for evaluation. Anxiety does not have to have a cause or reason. But it exists and needs treatment.
So, your brother needs to be seen and offered help as soon as possible by a psychiatric team including a psychiatrist, psychologist and others who may help him.
And siblings don't cause these types of things. You sound like you care and that's important. Let us know what happens.
He's 11? Prety young. I can't give a diagnosis; i would hope the hospital would of had him seen by a psychiatrist, they are the ones who specialize in these types of mental disorders. A diagnosis helps shed light and understanding on the problem and gives direction on what to do, how to handle it. Depending on the diagnosis, there may be medication that may help. Early diagnosis is key to a better overall result, studies have shown.
Also sounds like this is affecting you too, with concern for your brother, and having to deal with him in his current state. There may be a Mental Wellness Center nearby, or NAMI, or Mental Health Association, or something like that, which may have support groups for family members who have a mentally ill family member. There's a class called "Family to Family" that is popular here, which teaches about the common types of mental illness, what it is, and useful information.
Taking care of yourself is also a task that becomes important. Typically just having a group of people who understand, whom you meet with regularly, and can talk with, and tell them what's going on, just that alone can be very helpful, which is why so many support groups are formed on that principle. They don't have to fix your problem; them listening to your problem IS the cure it turns out. You still have the problem, but the emotional significance of the problem is diminished, so you can better live your life, and not be so disturbed by the problem.
If your brother's fear center has become overactive, he may fear everything, and need frequent reassurance that everything is OK, because his brain's fear center is telling him everything is NOT OK, even though there is nothing wrong around him. (No tigers are chasing him.)
You can research "Sympathetic Nervous System" and "Parasympathetic Nervous System." These are the "Fight or flight" mode vs. the "Rest Digest Restore" mode. Someone gets stuck in the "Fight or flight" mode, they react as if they are being chased by a tiger. It tends to shut down rational thought, pump adrenalin into the blood, which is all helpful if you are actually being chased by a tiger; and is disastrous in today's world where there are no tigers, but we stress over things and get us in that mode, and it's unhealthy to stay in that mode for long periods.
A lot of recovery, after finding medication that is helpful, is learning ways to get out of the "Fight or Flight" mode, and into the "Rest, Digest, Restore" mode, even if just for a brief time. Research Mindfulness Meditation", try some short guided meditations, it's a skill i was taught that actually helps, which mau be why people have bern doing it for thousands of years. There are some meditation apps. (Headspace is one. They have short animated videos on YouTube and their app that help explain the concept.)
School may have a counselor or sometimes English teachers are also good at this stuff and good to talk to. Or church pastors sometimes know of good resources. Budhist places often have free meditation groups and classes. Or some people prefer chanting which also seems to work.
Best wishes. Thank you for posting.