Great nephew. Your children are the first cousins of your niece and your children would be first cousins once removed. Your grandchildren and your niece's child would be second cousins.
The child would be your grandchild, and also your great great niece or great great nephew.
Your niece's child (your brother's or your sister's grandchild) and your grandson are second cousins to each other.
No. She is your great-grand niece
Your brother's child's children are your grandnieces or grandnephews.
Yes, it is possible. For example, if you were 22 when you had your child, and your child was 22 when she had your grandchild, and your grandchild was 22 when they had your great grandson, that would make you 66. When your great grandson was 21, you would be 87.
Great great aunt/uncle. To your niece, you are the aunt/uncle, to her child you would be the great aunt/uncle. So you would then be the great great aunt/uncle of her child's child (her grandson)
Cousins
You would refer to them as your nieces, thought they are formally your wife's nieces. And they would normally call you uncle.
Your nephew's children are your great nephews and great nieces (or grand nephews and grand nieces).
They are 2nd cousins.
Your sister's child and your grandson are first cousins once removed.
Your grandson's half-brother would be the son of your son's wife and another man. This means the child has no blood relation to your son and, thus, to you. If the child was not adopted by your son, then he would be your son's stepchild. By extension, you could call the child your step-grandchild, but this isn't really a commonly used word. If your son has officially adopted the child, he would be his adoptive son and, by extension, your adoptive grandson.
niece's - something that belongs to a niece. nieces' - something that belongs to multiple neices. nieces - plural form of neice. person who asked this question - an incredibly dumb person.
The word nieces' is the plural possessive form of the word niece (a female child of your brother or sister). Example sentence: Both of my nieces' birthdays are in May.
Your daughter and your niece's child are 1st cousins once removed.