I recently moved in with my parents due to my Mom's dementia and my Dad's decrease in mental status and disabilities. My Mom is very adamant that there is nothing wrong with her, yet she will call the police, and has done so several times in the past few months, to tell them she cannot set her thermostat or someone is "singing in her front yard" or "someone is spraying something in my yard". She has also gone outside in the dead of night in the Winter to see what the neighbors are doing and is constantly saying "they" meaning her neighbors are trying to take her property away from her. She says she talks to people living in her roof and argues with them to go away. Lots of times I will hear her talking to them but no one is there. One day she asked if I wanted to invite the people from inside the roof to eat dinner with us. She is capable of completing daily activities and her crazy PCP gave her an alzhiemers test which she did pass.The only real family around are my half brother who is diagnosed with paranoid schizophrenia and on medication and his wife who works in a doctor's office. My other half brother lives 1,000 miles away but has a son near here who is constantly here bribing my Mom out of money or anything else he needs. He recently got out of jail for the third time this past August and at 35 years old, refuses to work. He is also angry that I am living here because I think he wanted to move in here so Mom and Dad could support him. He has already threatened to "put a bullet in your head" and I am in the process of getting help to deal with that problem, but my Mom is in denial about him and thinks she has to do everything he asks. The nephew is totally aware of her mental condition and I guess uses that to his advantage. Mom refuses to see a doctor so I am in the process of contacting the Courts for conservatorship. I am 63 yrs old and trying to get into full remission for ovarian cancer, so all this is totally stressful. This is why I joined this website and I am so thankful for everyone here and have learned a lot already.
Sometimes our brothers get by with doing and saying things because there are no repercussions. If your brother threatens your life, it is assault and is prosecutable. If you feel endangered, please call the police and report it. You should not have to tolerate this because your parents feel that your brother should be able to do as he pleases without repercussion. I have the feeling you could tell us some stories of your childhood. There is a thread on Dysfunctional Families in the discussion section. It is rather long and hard to read through, but you can always post to the end. There are many children of dysfunctional parents here.
It sounds like a good choice to get guardianship or conservatorship. I know it will be a hassle, but your situation is a rather difficult one.