I'm going to name my son something my brother wants to name his own child.
Why would you name your son a name that your brother openly wants to use?
No. I want my child to have a unique name, I don't like how his name sounds
It's understandable that you want to have a unique name for your child but it's wrong to take someone else's name idea since they came up with it first. It's rude and inappropriate behavior that will strain your relationship with your brother. Instead of naming your own son with a name idea that your brother came up with, try to think of a good name yourself as it will be both more personal and meaningful to you.
I don't like the name he wants to name his own child. It will probably make his life miserable later.
Why would you want to use it if you dislike it? It seems like you just want to upset your brother and that's a horrible thing to do to a child, you shouldn't put your own son in the middle of your sibling rivalry.