My brother died of schizophrenia. It is caused by many factors, a genetic predisposition, low birth weight, premature birth, neurotransmitter imbalance, depression and loss events, and of course, the environmental aspects which do, in some cases exacerbate, (but not cause) the disease.
Also, there are so many factors in such a disease that many things about how some develop it, cope, and even grow out of it, are not yet known.
I wish your family the best. One of the biggest threats for all mental illness is public misunderstanding and stigma. Everyone in the modern world turns to some addiction to self medicate. FInding help means non-judgmental compassion, an end to misinformation, and a need to look beyond finding one substance, or addiction, to blame.