I'm going to prank my brother
Why do you want to prank your brother?
He doesn't live up to his potential
It's understandable to be frustrated with someone you think can do more, but it's not okay to prank family members in an effort to push them to do so. This might cause tension between you two. Try having a constructive conversation with them instead and explain to him how you feel.
I've tried to have conversations with him a few times but he just asked me to be nice to him. He's an adult, but people never change.
You should not try to change what he is. Let him be and try to get along with him instead of pulling pranks on him.