This is a very difficult situation. My concern is that your brother may act out violently toward members of your family. If he is actively using alcohol or drugs, then the risk of violence increases significantly. Do not hesitate to call the authorities if you feel that you or your family members are in danger.
You disagree with your brother’s understanding of his problems. He views his childhood as having been abusive. He may have a skewed view of that time. You described your childhood as having been “privileged.” Perhaps you are correct and he is wrong. On the other hand, he may have experienced abuse. It is not unusual, and it is in fact common, for parents to treat each child differently. Also, children can live in the same home and have completely different experiences.
Ideally, it would be best if your brother went to therapy. It seems as though he is dealing with many issues and his behavior is negatively affecting the family. If you have not suggested therapy, then you should.
If he is not agreeable to individual therapy, perhaps he would be open to family therapy. In family therapy, everyone works together to solve the problems. The onus is on the family to solve the problem rather than on just one member of the family.
If your brother is unwilling to change his behavior, then it is up to the people around him to change their behavior. That may not seem fair but you can only control your behavior, not the behavior of others. You and your family may have to develop a new set of rules for the home or the conditions in which you interact with him. A therapist could provide guidance regarding the best way to properly address your brother’s behavior. Please take care.