Why did Yahweh predict the gathering of his sons and daughters from the east and the west and announce to them earlier events?

Yahweh did this so that they might know him, believe in him and understand that he is God.

Is there any other god or savior than Yahweh?

Before Yahweh no god was formed and there will be none after him. He is Yahweh and there is no savior but him.