3rd cousin I think:-)
Mother's grandson as regards her daughter is either her (daughter's) son or her (daughter's) nephew.
Through marriage your step - sister's daughter is your step-niece!
Your nephew's daughter is your great niece and you are her great Aunt (or Great Uncle).Correction:Your nephew's daughter is your grand niece. You are her grand aunt or grand uncle.
If she's not your mother, that would make her your Aunt.
Your great grandparents brothers and sisters are your great uncles and great aunts.
Most likely they would not be related to you
3rd cousin I think:-)
Your daughter and your first cousin are first cousins, once removed.
Niece
your second nephew
Second cousins once removed.
First cousin once removed.
cousin
It says what relation are your brothers nieces to you.... It could be your child or your niece also causes you can have two brothers and it may be the other ones kids. Or of course it could be your brother's new wife kid by another man making her no relation.
Technically there is no relationship. When introducing her, you would refer to her as My daughter's mother-in-law.
3rd cousin
your step niece,,, if it was your brothers own daughter it would be your niece, since its his stepdaughter, than its your step niece.