Your grandfather's brother's daughter is your first cousin, once removed.
3rd cousin I think:-)
Niece
First cousin once removed.
cousin
She will be your aunty
3rd cousin
Two people whose grandfathers were brothers are second cousins to each other.
your step niece,,, if it was your brothers own daughter it would be your niece, since its his stepdaughter, than its your step niece.
They would be cousins, once removed.
Your great great grandfather.
i am my own grandfather
She would be your great grandmother