If you are a female you could be talking about yourself. You could also refer to a sister this way. This could also refer to a cousin of yours, since your aunt's husband may have nieces through more than one sibling (either his siblings or your aunt's siblings). It is not clear whether you are related to your aunt or to your uncle by blood, but it is very probably one of them and not both.
If your aunt is the sister of one of your parents, then her husband (your uncle) may have nieces who are not related to you at all. These would be the daughters of his siblings.
Your husband's niece is also your niece. (She will certainly call you her aunt.) Her husband might be called your nephew-in-law (if there was such a thing), but is most often called "my niece's husband," or, if you really like him, "my nephew."
The English language does not have a term for the husband of your niece, let alone of your step-niece. Most would say that you are not related.
Call him your niece's husband, if you have a need to refer to him.
There is no actual blood relationship. If it was your daughter's niece, you would be the grandmother. In most families, she would be referred to as a great niece, even without the blood connection.
Your niece's husband is not related to you. You would refer to him as "my niece's husband."
Your sister's husband is your brother-in-law. His niece is a child of one of his siblings, and is also a niece of your sister by marriage. There is no relation to you.
Your husband's niece is your niece and her son is your great nephew. You are his great aunt.
Your niece's husband is your nephew (by marriage). If you are male, you are his uncle (by marriage).
You're her aunt.
You would be a first cousin by marriage, in other words, there is no direct relationship between you.
Second Cousin
Great-niece.
Nephews and nieces
your 2nd niece...!
They are your nieces and nephews.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
He is their Uncle and they are nieces and nephews.
They would be great nieces or great nephews.
They are your great nephews and/or great nieces. Alternately, some people say grand-nephews, grand-nieces.
It says what relation are your brothers nieces to you.... It could be your child or your niece also causes you can have two brothers and it may be the other ones kids. Or of course it could be your brother's new wife kid by another man making her no relation.
The children of your husband's siblings are your nieces or nephews. Their children are your great-nieces or great-nephews.