All of the books, except The Book of Ether, were written by descendants of Lehi. They were a branch of the house of Israel. These books were written in the period 600 BC to 421 AD. The Book of Ether is the oldest of the books. It contains an account of the Jaredites, and it was written about 2000 BC, at the time when the Lord confounded the language of the people and scattered them over all the earth.
(See Ether 1:33, 35-36)