Yes. your sibling's sibling's child. Yes. 2 siblings. Basically your niece's first cousin is ur niece/nephew as well
Your sister's uncle is also your uncle.Your uncle's first cousin would be one of your grandparent's nieces or nephews, which makes them your first cousin once removed.The fact that this uncle is the oldest of your uncles makes no difference to the relationship.
Your grandfather's niece is a first cousin of one of your parents. Her son is your second cousin.
You do not have a niece-in-law. Some of your nieces and nephews are that because they are the children of your husband's siblings. They are your nieces and nephews and you and your husband together are their "aunt and uncle."
Your cousin's child is your first cousin, once removed. Then when that child grows up and has a child, it will be your first cousin, twice removed. Now, if you have a child, and your cousin has a child, your children will be second cousins to each other. Then their children will be third cousins to each other.
Second Cousin
Assuming both children are on the same side of the family, your child's first cousin is a second cousin to your first cousin's child. Your child is also a second cousin to your first cousin's child. Your child can have first cousins who are not related to your first cousin and thus not related to your first cousin's child.
All of your cousin's descendents are related to you. Your first cousin's grand chid is your first cousin, twice removed.
It does not appear that Thomas Jefferson had any nieces or nephews. He had a daughter, a son in law and two grandsons. He also had an aunt and a first cousin.
You would be a first cousin by marriage, in other words, there is no direct relationship between you.
Your first cousin's grandchild is your first cousin, twice removed.
Your mother's first cousin is your first cousin once removed.
Your grandfather's first cousin is your first cousin, twice removed.