The daughter of your husband's brother is his (and your) niece. Her daughter is his (and your) great niece.
no you have to say: my husband, my daughter and i ....
The daughter of your husband's brother is his (and your) niece. Her daughter is his (and your) great niece.
Your daughter's husband is your son-in-law.
Your daughter's husband is your son-in-law.
The daughter of your husband's brother is your niece.
Your husband's cousin is not related to you. His/her daughter is not related to you either.
Your sister's daughter is your niece. Your niece's husband is not related to you.
my cousin's husband
Your husband's step-daughter could be your daughter.Your husband could also have a step-daughter who is the daughter of a previous wife from her prior marriage to someone else. In that case, his step-daughter is not related to you, unless you adopt her.
Yes we can give zakat to our daughter if her husband is poor.
Since your sister's husband's daughter is usually your sister's daughter, you are her aunt or uncle. If the husband's daughter is from a prior marriage (before he married your sister) then the daughter is not related to you. However, if the daughter is young, her father may have her call you and treat you as an aunt or uncle.