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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.
You have your daughter. You can let go of your husband and live your life and be happy along with your daughter. Life is never meaningless. There's always something or someone that gives meaning to life for us.
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.