Your grandfather's first cousin is your first cousin, twice removed.
Yes, you are related to your grnadfather's first cousin. Your grandpa's first cousin is your first cousin, twice removed.
Your grandfather's niece is a first cousin of one of your parents. Her son is your second cousin.
Your daughter's grandfather's brother's son is her mother's or father's first cousin and her first cousin, once removed.
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.
cousin
Your grandmother is first cousins with cousin. Your parent would be the second cousin of the cousin's son. That would make you second cousins once removed.
All of your cousin's descendents are related to you. Your first cousin's grand chid is your first cousin, twice removed.
Your grandfather's cousin is your cousin twice removed. Her husband has no direct relationship to you.
Your mother's first cousin is your first cousin once removed.
Your first cousin's grandchild is your first cousin, twice removed.
3rd cousin
Your cousin's child would be your first cousin once removed. So, your cousin's adopted child would be your adopted first cousin once removed?