I took my sisters baby name
Why would you take his name? That sounds messed up.
He's a genius baby, I want to take his name
If your sister is fine with him, there is no problem. It can be flattering to take somebody else's name.
It takes a lot of pride to be called Nobel baby, I've earned it properly.
Your sister had the name first, so you shouldn't have stolen it. You should really try discussing it with her first, or else you'll disappoint the rest of your family.