Your sister's daughter is your niece and her granddaughter is your great niece.
Your sister's daughter is your niece, her granddaughter is your "great niece"... or you could just call her by name.
Your sisters grandson would be your grandnephew.
Your mothers sisters Granddaughter is your second cousin
Your granddaughter and your sister's grandson are second cousins.
Yes
Great neice
Your grand-niece.
Your son and your sisters child are first cousins. The granddaughter is out of synch by a generation. That will make them first cousins once removed.
If you find that your granddaughter has knots all over head you should call her parents. If you are her guardian, you should take her to see a doctor immediately.
Not sure but i guess it would be your great aunt's daughter
Your sister's granddaughter is your great niece and you are her great aunt (if you are a woman) or great uncle (if you are a man).
The half-sister of your granddaughter's half-sister is your granddaughter, or is not related to you.