The Weasley family
It is unknown when the Weasley family was started. It is likely that the first Weasley was Septimus Weasley, who married Cedrella Black and had three kids and two of them are unknown. Arthur Weasley was definitely one of their children.

Arthur married Molly Prewett who had two brothers, Gideon and Fabian, and you probably remember reading about their uncle, Ignatius Prewett in chapter one. You have definitely heard about Molly and Arthur's seven children, William, Charlie, Percy, Fred, George, Ronald, and Ginevra.
William, also known as Bill, married Fleur Delacour and they had three kids, Victoire, Dominique, and Louis. 
Charlie, on the other hand, neither married or had children.

Percy married someone named Audrey and had Lucy and Molly the second. 
Unfortunately, Fred passed away in the battle of hogwarts and did not marry or have kids. Although his twin George married Angelina Johnson, and had Roxanne and Fred the second.

And then Ronald, or Ron for short, married Hermione Granger and they had Rose and Hugo Granger Weasley.

That leaves us with Ginevra (Ginny) who married the famous Harry Potter and later gave birth to Albus, Lily the second, and James the second.