My parents did not set a healthy example for us as kids. they had lots of problems. one that my siblings now have also is brain tumor. how can i avoid getting it also?

Brain tumors: Brain tumors are genetic. While there is a slightly increased risk in the family members of patients with brain tumors, the overall risk is quite small, < 1%. Stress from your parents failings (we all have failings) did not cause a brain tumor. All you can do is to avoid environmental exposures that increase the risk--such as external radiation, even excessive head ct scans, etc.

Would not worry: Bad health habits can't really be a cause of a brain tumor. The closest i can think of would be to get a smoking related cancer and have brain metastasis. Avoiding that is easy.