I think you come out as who you are (all 3 of mine are utterly different, not startlingly like me or dh in personality etc). But I think nurture plays a huge part.
I was adopted but got to know bio mother in my early 30s. We are now close. We look like each other a bit. We have some traits in common - like we like to organise the same way, we are both more logical than emotional etc. but nothing startling. I suspect I may have gotten some of my intellectual stuff from useless bio-father but since he couldn't be bothered to ask to meet his own child, I won't know for sure.
What I do know is that my adopted sister (no relation) and I couldn't be more different but the way we live our lives is startlingly similar. We picked really really decent loving (although very different) men to marry (thanks Dad for showing us what a good man was like), we stay connected to family/cousins etc because we were shown that that was a good thing, we give to charity and try to help people because both parents made this a part of their lives every single day. We live the values of my parents even though none of us were related to each other.
Nature matters - a lot. I was better at school than my sister - nature, not nurture. She is slimmer than me and finds it easy to stay slim - nature, not nurture. But the things that matter - being kind, not putting up with shit in a partner, valuing ourselves, were all nurture.
Funnyfarmer I can see how your brother could have had an entirely different path if born into a different family
I really believe what ever life he was born into he would have stopped at nothing to be better than everyone.
In middle/upper class families this usually doesn't end up in a life sentence - instead the worst will be a spot of time for fraud.
I am sorry for the victims of his crimes and for him that this is where he ended up. It is why I think "there but for the grace of god go I" rather than "I deserve all of my good fortune".