Wait does that mean that girl isn't his niece...wait please someone explain

Maybe she got her mother family name for some reason..
Maybe his brother is already married and it's not possible to register her as a daughter or some other problem ╮(￣▽￣)╭

Nop she's clearly a niece and they have the same blood line ╮(￣▽￣)╭

But they way she stutters and answer seems to be a bit shady to me. I dont know tho