You haven't tried social services. I know there are horror stories about them but they are not out to take your kids. They can't take your kids without good reason, like sexual abuse or bruises all over their bodies.
A friend of mine, who recently passed away at age 42 (very sad story...unknown blood clot) adopted two kids. One was like your son and the police were always there. She never got arrested or threatened and they were able to calm him when she could not and her husband wasn't home. He lives in an Residential Treatment Center (RTC) now, getting the help he so desperately needs. The other kids are still home. The Residential Treatment Center (RTC) was my friend and her husband's idea when he started expressing sexual thoughts about little girls. He has a younger sister. Although your son hasn't done that (yet), he is dangerous to you and your daughter and should not be at home. The other chaos does not help him. It probably even makes him worse.
There is nothing you alone can do for your son. And your friend does not know how to deal with your son either. She isn't trained to do so. You need professional help or your future will be the police, all right, when your son is in jail and you can't hide it anymore. At least if you try, you can always tell yourself you did your best. The school is not able to take care of high needs child such as your son. He is too violent and out of control. They can not help him. They are educators, not psychiatrists. You have a much better chance of the school calling social services on you and you getting into trouble than if YOU do it first.
One thing no mother ever wants is to see her grown child in trouble and to think, "I didn't do enough" and really mean it. I know you are afraid, but this is for your son, not you, and it is not enough. He is getting worse, not better. Wait until he hits his teens. It won't be pretty. You will no longer be able to hide him or what is going on at home. Eventually, the authorities, either social services or the police, will find out. And if you didn't make the first move,t hey will assume you were covering up for something and may finger you as abusive. I've been a foster mom and dealt a lot with social services. They can be your friend or your enemy. But if you have a child who acts out so obviously, they WILL get to know you as will the cops.
In my friends case, the first time the cops came it was a neighbor who called when her son was running down the street screaming and swearing at her. The teachers started calling next, and then help from them became an ultamatim. The child's birthmother had schizophrenia. To this day, this child is so puzzling, he is not formally diagnosed. They suspect attachment disorder. But attachment disorder does not always apply only to adopted kids. If your son had a very chaotic early years with breaks in caregiving, abuse, and screaming, and neglect of any sort, he could have it too. Or he could have the biological makeupof his birthfather. Only YOU know what his birthfather was like to know if this is possible.
Just like you either will have to calm down your every day life or be sick very young, you will eventually have to meet the cops and social services because your son is violent and it won't get better when he is older. He is vulnerable to taking drugs, stealing, doing all sorts of things that will get him into trouble. Just like you are not a professional caregiver and can't adequately take care of your entire elder family, you are not trained to take care of your son and his problems without help. And you'll get the help, either because you ask for it or against your will. Eventually, especially as he gets older, he will come to the attention of some authorities that you don't trust. It may be best to build a relationship that you CAN trust earlier rather than later. One day your son will assault a teacher or neighbor or friend or maybe even a cop and he will be more like fifteen and tall and strong and it won't be overlooked, Know what I mean?? It won't fly.
Just a suggestion.
As always, hoping you can break down that wall and make your life better. By doing that, you make everyone you love more accountable for his/her own life and they are better off for it. It isn't good for anyone to be so dependent on somebody else. What if the person suddenly isn't there anymore?
My 42 year old friend did not expect to die. Fortunately her husand is a strong man, but you are alone. You need to keep yourself healthy, fit and happy. THAT is what is best for you and for everyone you love. No matter how much Family guilts you out or how scared you are of authority figures, for whatever reason, if you don't take action yourself...action will be taken against your will. Life does not stand still. It changes. I hope you can stop being so afraid of everything and so beholden to those who are making things worse, and do what you need to do to help your son and daughter and YOU. Yes, YOU MATTER.