Second Nephi 25:12
But behold they shall have wars, and rumors of wars; and when the day cometh that the Only Begotten of the Father, year, even the Father of heaven and Earth, shall manifest himself unto them in the flesh behold, they will reject him, because of their iniquities, and the hardness of their hearts and the stiffness of their necks.
Now this is peculiar indeed. Why, because essentially Mormon’s see no difference between Jesus and us. We are all children of God. Jesus and Satan are our brothers. God has begotten us all. So Jesus really isn’t the only begotten son of God. They interpret this to be a cliché by which is meant a special, unique child, a beloved child, but not an only child. I’ll let them explain:
So, what does “only begotten” mean when speaking of sonship in this kind of context? The Greek term mon-og-en-ace’ (commonly translated as “only begotten”) was intended to denote that a son was unique, special, and of particular endearment4—which would set him apart from other sons.
Given these facts, we can ask the question, “Could this meaning also apply to Jesus’ relationship to God the Father, being unique, special, and of particular endearment, thereby allowing a belief which includes Jesus having siblings?” Certainly.
The Church of Jesus Christ of Latter-day Saints teaches that Jesus is the spirit brother of both angels and all mankind. Before you and I were born, we lived with God the Father and our brother Jesus Christ. It is true that Lucifer was a son of God. It is also understood that he became prideful and rebelled against God. In consequence of his actions and unwillingness to accept the Father’s plan, Lucifer was cast out of Heaven.
The link will bring you to the full tract put out by fairlds.com. It is an interesting piece. To say the least with interesting spins. That the word is used as unique and beloved in other works does not mean that it is being used the same way in the New Testament, or in relation to Jesus Christ and the Father. There are but a few problems with the Mormon doctrine concerning the sonship of Christ, and the word monogenace, or Only Begotten. For one it makes Christ anything but unique. So there is a catch 22 in the acceptance of their definition. It makes Christ no more than one of us, a child of God.
Christian do believe that all mankind are children of God in the sense that God has created us. We believe that God loves us, and this is why he sent his Only Begotten Son to die for us. But we recognize that our relationship to the Father is radically different than the one Jesus has with the Father. We even recognize this in our unwillingness to call the Father, as Jesus did, “My Father.” We call the Father after the manner Jesus taught us when he taught us to pray “Our Father.” Even if a child is a bit favored by a father, he does not refer to the dad as “my” father, in front of his siblings. Jesus referred to the Mather as His Father many times. "Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven. (Matthew 7:21 (ESV) The Jews understood the meaning of this well, as it is explained in John 5:18:
“This was why the Jews were seeking all the more to kill him, because not only was he breaking the Sabbath, but he was even calling God his own Father, making himself equal with God.” (John 5:18 (ESV)
The fact that Jesus is equal to the Father is the reason John spends so much time in the first chapter explaining the relationship between the “word” and the Father. The most definitive article on the Meaning of Begotten is by Büchsel, found on pages 737-741 in the fourth volume of “The Theological Dictionary of the New Testiment.” Edited by Kittel. It leaves no room for doubt that John’s use of the term “Only Begotten.” Was meant to be taken literally.
The upshot is Mormons don’t really believe that Jesus is the only begotten, despite the use of this term in the Book of Mormon, which they can only use after radically redefining the term despite the fact that there is no contextual reason to do so, and very many good contextual reasons to read it in its plain meaning.