I'm not sure why your other psychiatrist said that the Schizophrenia was caused by stress. If that were possible, then a lot of people would have Schizophrenia. It may contribute, but it is, as far as my experience, not a direct cause.
Researchers have found that there is evidence of an imbalance of chemicals. It can also be as a result of genes, especially if the relative is a first degree relative like a parent, sister or brother. Here is an article on it from the National Institute of Mental Health:
This article can help explain where researchers think Schizophrenia came from. Here is another link to help you:
The more you understand the more you can help yourself.
It sounds like there is certainly something going on with your Uncle and maybe your dad and Aunt. It could have been abuse or it could be mental health symptoms. But to have Schizophrenia they would have to have the symptoms probably similar to what you have now.
We need to start a new thread here if you have more questions.