A
That's very sad news. Sorry to hear about your father Ariel. God be with you in this hard times. Mental illness sometimes is genetic but sometimes it is acquired through the bad choices one makes like taking drugs and drinking alcohol. This is what the Bible says that sin always have consequences. To sin is to self destruct because we become more open to the attacks of demons.
However I do NOT believe in blaming demons for every sin humans commit.
I believe those truly possessed by demons are not in control of their physical body and their soul cries out for deliverance, which any Holy Spirit filled believer can give them by clearly proclaiming the gospel and having them accept Jesus as their Lord and Savior.
However, I believe mental illness is not the same as demon possession, though people often mislabel one of the other.
Mental illness is a physical illness of the mind and like a physical illness of the nervous system or the heart or the blood. I believe someone with mental illness is like someone who is confined to a wheelchair. If that makes any sense.
I do believe that demonic possession can cause physical illness. But not all physical illness is demonic possession. Also not all demon possessed people display physical illnesses.
Satan is called an angel of light and his minions pose as ministers of righteousness.
So it's a complex topic.