I understand that you and your family can't get him in for treatment. However, getting a "dealing with schizophrenic family member" book (or something similar) might be helpful for all of you. I found this book on Amazon: Surviving Schizophrenia, 7th Edition: A Family Manual. I don't personally have this book or know the author, but it reviews well and looks informative.
I took a Psychopathology class in grad school and schizophrenia is really a sad illness. It's not something that was nurtured, but rather something a person "gets" (nature). They can't help what happens to them and there is no cure - only treatment. Additionally, it is very painful for family members and they endure severe collateral damage from this illness.
You and your family could really benefit from your own therapy to help deal with your brother's illness - regardless of his "official" diagnosis or not. Hugs to you all.
The website schizophrenia.com is a great resource. They have a page about schizophrenia symptoms, including the criteria for diagnosis in the US: http://schizophrenia.com/diag.php
They also have a page on First Aid for Psychosis: http://www.schizophrenia.com/sznews/archives/005561.html
Some excellent books are available on Amazon:
https://smile.amazon.com/Surviving-Schizophrenia-7th-Family-Manual/dp/0062880802
https://smile.amazon.com/Complete-Family-Guide-Schizophrenia-Helping/dp/1593851804
You can also find memoirs about schizophrenia by searching Amazon for "schizophrenia books" and refining your search on the left bar menu to Department: memoirs.
If you want to read my memoir in progress, it's free on my google drive: https://docs.google.com/document/d/1sZE46cXq0BBGtQd2N_VOEkRqvL3dVv6hJ8uJAH204a0/edit?usp=sharing
Maybe it would be helpful to check in with him regularly about how he would like you to help. He might not have any idea most of the time, but sometimes he will know what kind of support he needs, and if he knows that you’re willing to hear his needs, he’s more likely to come to you.
There is a ton of good literature out there about how to support loved ones with mental illnesses and chronic illnesses. Here’s a link to a book that was recommended to me (although I haven’t read it) https://www.goodreads.com/book/show/190040
https://www.amazon.com/Surviving-Schizophrenia-7th-Family-Manual/dp/0062880802
Also check out “The Center Cannot Hold” by Elyn R Saks. It’s more of a memoir, but really fascinating. It’s also a great example of someone who is thriving with schizophrenia.
Having spent an entire year on a psychotic spectrum detail in 2014-15, and being intimately familiar with psychotic bipolar I as well as the schizopherniform disorders, I have to suggest that trying to take responsibility for the behavior of people with transient psychosis is beyond the capacity of most professionals, let alone those who haven't been through extensive and intensive post-graduate education and training. The very best you can do is a) do what you can to make sure she's on the local social services radar, b) stay on her about taking her oral meds, and c) see if they can get her to go on depot medication.
I would also get a copy of this book and this book... and read them cover to cover.