A boy and his mother's first cousin once removed are second cousins or first cousins twice removed. Which it is depends on whether the mom's first cousin once removed is the child of her first cousin or the mother of her second cousin.
My first cousin, Mary, has a son, David, who is my 1st cousin, once removed.
He is my daughter's 2nd cousin.
Your father's brother-in-law is either the brother of his wife (your mother) and thus your uncle, or he is the husband of your father's sister, and thus your uncle.
The son of your uncle is your first cousin.
If the brother-in-law has a son from a previous marriage, before he became the husband of your aunt (if that is how he became the brother-in-law) that son is not related to you.
cousin... the fathers sister is the 1st boys aunt. any children the aunt has is the 1st boys cousin.
The son of a woman's husband's brother is the woman's nephew and she is his aunt, as long as she remains married to her husband.
The son of a first cousin is a first cousin once removed.
You and your first cousin's son are first cousins, once removed.
your son and your brother's son will be cousins
your son and your brother's son will be cousins
your son and your brother's son will be cousins
second cousins to his cousin's children, you'd be third cousins
Your son's child and your nephew are second cousins.
Your granddaughter and your niece's son are second cousins.
Your son and your aunt's child are first cousins, so your son and your aunts grandson (the son of your aunt's child) are first cousins, once removed.
He would be your second cousin.
Cousine
First cousins
First cousins