'Great aunt' and 'Great uncle' are what your children properly call your own aunt and uncle. Your aunt and uncle are the brother and sister of your parent. Your parent is your children's grandparent.
If your a boy they would call you great uncle, if your a girl they would call you a great aunt.
The children of your husband's sister are your nieces or nephews, and you are their aunt, just as he is their uncle.
Your brother's children call you their aunt if you are female, or their uncle if you are male. Their are your nieces and nephews.
Your niece will call you her aunt or uncle.
In English, you call your maternal uncle's wife "aunt." It's not rocket science, honey. Just like how you call your paternal uncle's wife "aunt," keep it simple and call her the same thing.
You are a great great Aunt (or Uncle) to the grandson of your Nephew.
your uncle
Boys = "nephews", Girls = "nieces". If you are a man they will cal you "uncle" If you are a woman they will call you "aunt" or "auntie".
Great Aunt/Uncle
In most families they would call you aunt or uncle. It would technically be great aunt or great uncle.
Your uncle or aunt's children are called your cousins.
If the children of your great uncle's wife are also your great uncle's children, then they are your parent's first cousins, and your first cousins, once removed.If your great uncle's wife has children from a previous marriage, they are not related to you because you have no common ancestor. However, if they were very young when their mother married your great uncle, it may be convenient to treat them like "members of the family" and call them your first cousins, once removed.