That will make them second cousins. First cousins share a common grandparent. Here the children share a common great grandparent.
The grandchildren of siblings are second cousins to each other.
The grandchildren of your grandmother and the grandchildren of any of her siblings (including of her brother) are second cousins to each other.
Two people whose great grandparents were siblings are third cousins to each other. The children of siblings are first cousins. The grandchildren of siblings are second cousins to each other. The great grand children of siblings are third cousins to each other.
Your father and your aunt are siblings (brother and sister) The grandchildren of siblings are second cousins to each other.
Your grandchildren and your grandniece are second cousins to each other..
Your niece and your son or daughter are first cousins. That would make your niece and your grandchild first cousins once removed. Your niece's child and your grandchild are second cousins.
Your grandchildren and your great niece are second cousins to each other.
The relationship between two second cousins is that they are second cousins. That means that one of the parents of one was the first cousin of one of the parents of the other; and that one grandparent of one was the sibling of the grandparent of the other.
If two people have grandparents who were siblings, then their parents are first cousins and they are second cousins.People whose grandparents are siblings are second cousins.
Second cousin once removed are not at all like fourth cousins. With second cousins once removed, the two people have common ancestor. That ancestor is great grandparent of one and the great great grandparent of the other. Fourth cousins are the great great grandchildren of siblings, so they have a great great great grandparent in common.
There are many kinds of relatives. The most important are your parents, your children, your grandchildren and your siblings. Other relatives are Aunts, uncles, grandparents, first cousins, second cousins, great grandparents, etc., etc.
She would not be. You uncle's children are your first cousins and his grandchildren are your first cousins, once removed. Your children and your uncle's granddaughter are second cousins to each other.