I’m sorry you and your brother have been through so much and been so damaged. I experienced an abusive up bringing and I know it never leaves you, and shapes who you are for the rest pf your life. For me i was lucky and it shaped me to try to be a better person then my parents and not repeat their mistakes; it sounds like you are also treading that path.
My siblings were not so lucky, they are all damaged and have been unable to live “normal” lives. I lost one brother who died through severe mental illness, another sibling is crippled by mental illness and another is struggling but fortunately getting by.
I’ve learnt the hard way that you can’t fix other people, no matter how clearly you see what is going wrong. You can encourage people to deal with their problems, and you can support them when they try but ultimately they have to want to change or get better. Everything else you do, no matter how well intentioned, will not change anything if the person themselves does not see the problem or want to change.
Regarding your brother, you can reach out to him and try but sadly you may have to accept his life is stuck on a trajectory of self destruction and even sadly violence. I don’t think anyone is born bad, but are shaoed by their childhood. Your step dad and mum are also likely products of bad events or difficult up-bringings and it sounds like they couldn’t change their life paths either. Its a cycle of chaos and tragedy disrupting each generation.
But there is something you do have control over and can change - your own family. You can break the cycle by being a good parent to your children. You are now in the position your mum and dad were, and can be the role model for your kids and ensure they have a happy childhood. That is where you should focus your time and effort.
I’m sorry for your brother, despite his crimes, but your priority should be your wife and children and everything you do has to be focused on what is best for them. Sadly, if that means not including your brother in your lives then so be it. Be there if your brother reaches out for help but otherwise I think your time and energy is best focused on giving your children the upbringing and future denied to you as a child.
You succeeded despite your parents. Ensure your children succeed with your help and support. That will break the cycle in your family and that love, kindness and compassion will be felt by your grand children and great grand children. That is what you can realistically control and that could help many more than one person in your family long term. That choice could have positive echoes throughout your children and their children’s lives.
The oldest intact building in my city is from 1320 - so 700 years old. Baguely Hall, which is an old landowners hall.
The city itself - Manchester - dates back to the roman era and we have the remnants of an old castrum/fort in the city centre dating back to 79 AD - so 1945 years old. Surprisingly there were more complete ruins at the site but much of it was levelled during the industrial revolution.