Niece
Isabel is the younger daughter. Sam is the elder.
If he is your brother in law then his sister is your sister in law. So your sister in law's daughter would be your niece.
Your sister's daughter is your niece and you are her aunt (if you are a woman) or her uncle (if you are a man).
Aishwarya Rajinikanth
Your sister's husband is your brother in-law, there's no different word in english to describe the husband of an older or younger sister.
miley s sisters name is shuanny she is just like miley
Your daughter's step-sister would be your step-daughter.
Your aunt's daughter is your first cousin.
Grandaughter.
neice
Your sister's daughter is your niece, her granddaughter is your "great niece"... or you could just call her by name.
Your sister's son is your nephew.