Mormonism teaches that God has a wife in heaven, and produces spirit children with her. Mormonism teaches that you, me, Satan, and Jesus are thereby spirit siblings who were born to them. In this way, Jesus and Satan are literally brothers.
Mormonism's Official Curriculum Material etc.
• “All men and women are literally the sons and daughters of God … Every person who was ever born on earth is our spirit brother or sister. Because we are the spirit children of God, we have inherited the potential to develop His divine qualities. Through the Atonement of Jesus Christ, we can become like our Heavenly Father…”[Gospel Principles, Chapter 2: Our Heavenly Family (2011)]
• “Elohim is literally the Father of the spirit of Jesus Christ and also of the body in which Jesus Christ performed His mission in the flesh…” [First Presidency and Council of the Twelve, “God the Father,” compiled by Gordon Allred, (1916), 150.]
• Joseph Fielding Smith(Mormonism's 6th president-prophet): “Man, as a spirit, was begotten and born of heavenly parents, and reared to maturity in the eternal mansions of the Father, prior to coming upon the earth in a temporal [physical] body” [Teachings of Presidents of the Church: Joseph F. Smith(1998), 335.].
• Bruce R. McConkie (LDS ‘General Authority’): —“A plan of salvation was needed for the people of earth so Jesus offered a plan to the Father and Satan offered a plan to the father but Jesus' plan was accepted. In effect the Devil wanted to be the Savior of all Mankind and to 'deny men their agency and to dethrone god,'” … “Jesus Christ, Lucifer, and all of us were spirit children of God in the pre-mortal world” [Mormon Doctrine (1958), 193, 278.]
Bruce R. McConkie (LDS ‘General Authority’): “The Father begets; the Son is begotten; they are Parent and Child” [Doctrinal New Testament Commentary, Vol. 3, 138.]
• Orson Pratt (A 'Quorum of Twelve Apostles' original member): “If none but gods will be permitted to multiply immortal children, it follows that each God must have one or more wives. God, the Father of our spirits, became the Father of our Lord Jesus Christ according to the flesh” [The Seer, 158.]
“The difference between Jesus and other offspring of Elohim[Mormonism's personal name for “God”] is one of degree not of kind.” [Doctrine and Covenants 93:21] Mormonism's Official Curriculum Material
• “The first spirit born to our heavenly parents was Jesus Christ …, so he is literally our elder brother (see Discourses of Brigham Young, p. 26). Because we are the spiritual children of our heavenly parents,…” [Gospel Principles (1997), 11]
• James Talmage(Quorum of the Twelve Apostles member): “[A]mong the spirit-children of Elohim, the firstborn was and is Jehovah or Jesus Christ to whom all others are juniors ... Human beings generally were similarly existent in spirit state prior to their embodiment in the flesh. …There is no impropriety, therefore, in speaking of Jesus Christ as the Elder Brother of the rest of mankind.” [Articles of Faith, 425-4266.]
• Bruce R. McConkie (LDS ‘General Authority’): “Christ, the Firstborn, was the mightiest of all the spirit children of the Father.” [Mormon Doctrine, 590.]
• Spencer W. Kimball: “The importance of not accommodating temptation in the least degree is underlined by the Savior's example. Did not he recognize the danger when he was on the mountain with his fallen brother, Lucifer, being sorely tempted by that master tempter?”[The Teachings of Spencer W. Kimball, 163.]
• Bruce R. McConkie (LDS ‘General Authority’): “The appointment of Jesus to be the Savior of the worlds was contested by one of the other sons of God. He was called Lucifer, son of the morning. Haughty, ambitious, and covetous of power and glory, this spirit-brother of Jesus desperately tried to become the savior of mankind.” [Mormon Doctrine, 193.]
• Bruce R. McConkie (LDS ‘General Authority’): “He is our Father in heaven—the literal and personal Father of the spirits of all men. He begat us; we are the offspring of Heavenly Parents: we have an Eternal Father and an Eternal Mother. … Christ was the Firstborn of all the heavenly host; Lucifer was a son of the morning: each of us came into being as conscious identities in our appointed order; and Christ is our Elder Brother.” [The Mortal Messiah, vol. 1, 21]