OP, further to my earlier post, I struggled with the grief that my DSs wouldn't know him as well.
DS1 was 9 months when my brother passed and DS2 came along in 2014 so never met him at all. I very much struggled after having DS2 as I couldn't fathom that two souls I loved more than anything, would never meet. It was so utterly unfathomable to me.
But my boys talk about their uncle ALL THE TIME (they're 10 & 8 now). My brother was a musician, loved music, had a couple of albums, and my kids ask to hear it all the time. We watch videos of him and I have a box of memories of my brother, the items of clothing he bought DS1 when he was born. I guess we've done this so much since they were babies that they feel they know him.
We live overseas so when we visit the UK, they see all pictures of him, of us as kids all over my parents home. We're still very close with my SIL and she comes and spoils the kids all the time.
We've kept him alive by never shying away from speaking his name, we tell stories about him, my sister and I laugh at memories that the kids hear. So I think they've formed this picture of what he was like, and my sister in law tells them about the things he loved which they adore hearing. They argue between each other as to which of them is most like my brother, DS1 thinks it's him because they both love spaghetti bolognese, DS2 thinks its him because he loves the guitar.
So there are ways to keep your brother alive, and it does get easier to do this as the years pass.