Troubled 11yo Child

I have two children adopted internationally. My eldest, 11 yrs, though adopted as a young infant, has had a serious of health and emotional difficulties, which started when he was five and his sister came into his life, but really got bad when he was about 8. He does well academically, and has tested as gifted, but socially and emothionally he really is like a two year old. He is very self centered, and though initially makes a good impression, does not have healthy friendships, largely because other children lose interest in playing with someone who is so self absorbed. At home, he has violent and destructive temper tantrums, makes threats of violence and I fear the day that I cannot physically restrain him to protect myself or our youngest. One of those terrible mass shootings occured in our community and he has expressed both fear of being killed, as one of the victims was born just a few days after him, and also of attacking and killing others someday. He has been evaluated by a very good psychiatrist, and we are seeing a very good family counselor, which is really our only source of support. He has a lot of anxiety and is doing better with an antianxiety medication. Regarding a diagnosis, ODD, attachment disorder, and antisocial personality disorder have been mentioned, but he doesn't 'fit' the categories in any definitive way. Even though he is very self absorbed and low on empathy, I really don't think he has antisocial personallity disorder. I think it is an attachment disorder and fear of not having enough from when he was starved. He was low birth weight, no prenatal care, and did not gain weight his first six weeks of life, though now he is obsessed with food and is quite overweight. He definitely has issues with attachment - he is fearful that something may happen to my husband, his sister or to me, and he also rages against us for taking us away from his birth family and country. He lies a lot, he steals, and he just likes to go through other peoples belongings out of curiousioty, stating he can't help himself. This morning I spend 40 minutes looking for my car keys, which had been in my purse, butI found in his undewear drawer, and was late for work. Sometimes he will confess sincerely and want to make amends. Other times he lies in the face of evidence. My husband and I are so worried about him, and also the effect of his behaviour on our younger child. I just pray for strength and that we can help him develop empathy and learn better social behaviors. He does better with consequences that are immediate, but not necessarily draconian (temporary loss of privileges with electronic media), but also making amends - repairing or paying for replacment of his sister's toys that he has destroyed, etc. and spending time in with family rather than out with friends. He is obsessed with buying new things, but destroys most of what he gets. I am so worried about him. I love my two children so much, they are the most wonderful things that happened to me. Have any of you had these experiences? What did you do? Thanks Siobhan