Are your sister's son and husband's sister's son related?
Your sister's son is not related to your husband's sister's son,
because they share no common ancestor.
What is your sister's daughter's son to your son?
Your sister is your son's aunt. Your sister's daughter is your
sons first cousin. Your sister's daughter's son (your sister's
grandson) is your son's first cousin, once removed.
Is your sister's husband's sister's son related to you?
No. Your sister's husband is your brother-in-law, but his sister (and her son) are not related to you. However, that son is your sister's nephew.
What is your sister to your daughter's son?
Your sister is your son's aunt. Your sister's daughter is your
sons first cousin. Your sister's daughter's son (your sister's
grandson) is your son's first cousin, once removed.
What is sister son called?
Your sister's son, is your nephew.
What is relation name for your husband's sister's son?
Your husband's sister's son is your nephew, just as your
sister's son is your nephew.