Granddaughter
Your grandson.
You call your daughter's baby, your grand-duaghter.
You would call your sister's daughter your niece.
They'd be your cousin.
Your grandson.
Your grand daughter's husband is your grandson-in-law.
Your niece's daughter is your grand niece, or, as some would say, your great niece.
when was lil Wayne daughter born and how old she is
I believe it is your cousin-twice-removed. Definitely your cousin-once-removed's daughter.
You should write daughter's if you are talking about one daughter, e.g. "it is my daughter's birthday tomorrow".You should write daughters' if you are talking about more than one daughter at the same time, e.g. "this is our daughters' bedroom, which they share".
would it be a brother in law? not sure about this one! Is it your husband/wifes daughters brother?
would it be a brother in law? not sure about this one! Is it your husband/wifes daughters brother?