A parenting expert once told me that it's important that parents have a 'solidly positive story' about their children. Internally as well as externally.
That doesn't mean excusing behaviour or condoning anything. It means that the story you tell yourself, them and the world is solidly positive.
Take DD. If you look at her one way, she's pushy, bossy, loud, terrible at risk assessment, hard to get along with, and lacks focus. Exactly like I was when I was young and my mum still has that story about me.
However, how I see DD, and how I describe her to her, and the rest of the world is; brave, kind, unique, enthusiastic, funny, interesting, passionate, good (not nice, good), a deep thinker, a good friend, a citizen of the world, and the literal best person I have ever met. Our childhoods are going very differently so far.
Think about your son in terms of what he offers, what he's good at, what he values. Form a solidly positive story about him. Your brother is nothing to do with your son. He is his own person and forming that story means he will live that story, the good story.