It is believed that schizophrenia has a genetic component, but that does not mean that the offspring of people with schizophrenia will develop the illness. The increased risk for the offspring is slight. There are many other factors that would need to be present for schizophrenia to develop. Genetics is only part of the story.
The majority of people who develop schizophrenia have experienced trauma, often many traumas, throughout the course of their lives. Drug use is also a factor as are many other psychosocial factors including stress, head injury, and so forth.
The fact remains that there is no certainty about the causes of schizophrenia or any other mental illness. Differing theories exist, but there is no universally accepted answer. It is unlikely that you will receive a definitive answer to your question. Science, at this point in time, cannot provide those answers.
There is no guarantee that your children will not develop schizophrenia but based on the information you have provided, the probability is very low, perhaps no more so than anyone without your family history. Your fear about their developing schizophrenia should match the actual, factual probability that exists. Your fear should be minimal.
All of us should strive for psychological health. You and your husband should strive to be as psychologically healthy as you can be for your children, should you choose to have them. That means that if you or he believed that something was psychologically wrong, then the proper course of action would be to seek treatment from mental health professionals. That’s the best way to protect and preserve psychological health.
Evidence-based mental health treatments exist and are very effective. The problem isn’t treatment ineffectiveness; it’s that many people who have mental health problems don’t seek treatment for them. There are many reasons why people don’t seek treatment, but stigma is chief among them. Many people erroneously believe that seeking mental health treatment is a sign of weakness. It is a sad fact that many people are needlessly suffering with treatable conditions.
You said that you and your family have “never encountered a schizophrenic that didn’t deteriorate into oblivion.” That is not my experience, and I’ve worked with many people with schizophrenia. Research shows that people with schizophrenia who participate in treatment can live high-quality and fulfilling lives. Elyn Saks, a UCLA psychiatrist, is one example that comes to mind. You might try reading about her story.
Your fears about having children who will develop a serious mental illness (SMI) seem to be inconsistent with the reality of the situation. Only 6% of the United States general population has an SMI (i.e. schizophrenia, bipolar disorder or major depression). You might consider counseling to help you address your fears and to align your feelings with reality. Please take care.