Lots of people (in fact by far the most of drug abusers) never go on to develop schizophrenia. So while you may be right that it has been a trigger for your brother - its likely just the most recent factor that tipped the balance of his risk for schizophrenia.
Most of the research now says that its a biological / genetic risk that happens first - and then other factors push the person into psychosis - it could be stress (many people do drugs to relieve depression or anxiety which are highly stressful). To put it simply - its complicated, and its impossible to know in advance whether you or anyone else has these predisposition to schizophrenia - so you can’t really blame the person for it.
Here is some related reading:
More details on the Causal Factors in Schizophrenia, and How to Prevent Schizophrenia (relevant for the rest of your family and children and future children:
Causal Factors:
Preventing Schizophrenia: