Can your father's sister's son be your brother?

Answer 1

It is physically possible for your dad to also be your cousin, but it is socially unacceptable and also illegal. Your dad would have to have been your uncle or aunt's child. That would mean your mom fooled around with her Nephew. That is called incest and is illegal in most parts of the world.

Answer 2

No. Your father's sister's son is your first cousin. However, there is an interesting phenomenon which can happen if your father and sister marry two siblings. Your father's sister and your stepmother's brother's children become your double first cousins, because they are both your father's sister's children, and your (step)mother's brother's children.

Answer 3

Only if he marries your aunt.

Or, similarly, if one of your parents had a child by one of your grandparents, making their son also their brother. He would be both brother and uncle to his siblings.

Answer 4

Certainly. If you and your sister have at least one other sibling, and that sibling has a son, he is your nephew and your sister's nephew.