Nephi L. Morris, in a discourse delivered in the Salt Lake Tabernacle in August 1908, teaches Adam-God and the existence of both a Father and Mother in Heaven.
Nephi L. Morris, "Infinite Possibilities of Man," A Discourse Delivered in the Tabernacle, Salt Lake City, August 9, 1908, repr. Deseret Evening News (August 15, 1908): 25
PRE-EXISTENCE OF MAN.
The Latter-day Saints do not believe in the modern ideas of man's origin from the protoplasm cell, the theories of evolution which is not always clearly defined even by the scientists themselves. The Latter-day Saints believe that man is an eternal being, co-existent with God; that we are the children of the Deity in nature and in endowment and in attributes like unto Him. That we were begotten of Him, not in this life, but in a life when preceded this. We believe that Adam and Eve, our first parents, were human beings who had attained to exaltation and immortality in some other earth-like experience and when they had advanced to a condition in which they found themselves prepared to people an earth and preside over it, this earth was prepared for them and they came here as living beings and peopled it by their own progeny. But to our individual experiences I wish to refer, more particularly, in the life which preceded this.
We believe that we were all the children of God in a life which ante-dated this one, where we lived in the immediate presence of our heavenly Father and our heavenly other, if you please—for this is a principle of belief peculiar to the Latter-day Saints, that God the Father has associated with Him, God the Mother, whose children we are. We dwelt with them in the kindergarten department of God's great university, as we might term it. We had progressed by learning the lessons of that life until there was no room for further advancement and progress there, and the Lord in His economy, desiring to promote the welfare and bring to pass the exaltation of all His children, conceived a plan by which we were to be permitted to live upon this earth, as mortal beings.
. . .
We lived before we came to this earth; we shall live forever; and by the blood of Jesus Christ, and the means of salvation afforded through Him, we shall go on and on from the very kindergarten of our beginning, even to the graduation day, wherein we shall become Gods, when we shall become an Adam and Eve, and shall be planted upon an earth where we shall become the progenitors of a race of human beings over whom we shall preside as fathers and mothers—as Gods, if you please.