No, you would call him your recently departed husband, or your deceased husband.
You would call your sister's husband your brother-in-law.
You would call your aunt's husband "uncle".
In Zulu, you would call your husband "umkhwenyana."
Your husband's niece is also your niece.
sister
The English language has no term for a relationship between you and your husband's sister's husband. Most people would not consider her to be related to you. You could call her your sister-in-law's husband.
Your sister's husband is your brother-in-law, but in conversation you would not use that term as a title, but would call him by name.
Unless you are in a polygamous marriage, you are your husband's wife, so you would call her your mother.
How about your brother.
The sister of your husband is your sister-in-law.
The English language has not special term for the husband of your sister-in-law. You woudl call him your "sister-in-law's husband."