The fleshly body of Jesus required a Mother as well as a Father. Therefore Father and Mother of Jesus, according to the flesh, must have been associated together in the capacity of Husband and Wife; hence the Virgin Mary must have been, for the time being, the lawful wife of God the Father...” Apostle Orson Pratt The Seer, Oct. 1853, page 158
The birth of the Saviour was as natural as are the births of our children; it was the result of natural action. He partook of flesh and blood—was begotten of his Father, as we were of our fathers.” Brigham Young Journal of Discourses, vol. 8, p. 115
Christ was begotten by an immortal Father in the same way that mortal men are begotten; and Son means son. Christ was begotten by an Immortal Father in the same way that mortal men are begotten by mortal fathers.” Mormon Doctrine, 1979, pages 546-47 Apostle Bruce R. McConkie
It was also lawful in Him, after having dealt with Mary, to give her to Joseph her espoused husband. Whether God the Father gave Mary to Joseph for time only, or for time and eternity, we are not informed. Inasmuch as God was the first husband to her, it may be that He only gave her to be the wife of Joseph while in this mortal state, and that He intended after the resurrection to again take her as one of his own wives to raise up immortal spirits in eternity.” The Seer, Oct. 1853, pg. 158
The birth of the Saviour was as natural as are the births of our children; it was the result of natural action. He partook of flesh and blood—was begotten of his Father, as we were of our fathers.” Brigham Young Journal of Discourses, vol. 8, p. 115
Christ was begotten by an immortal Father in the same way that mortal men are begotten; and Son means son. Christ was begotten by an Immortal Father in the same way that mortal men are begotten by mortal fathers.” Mormon Doctrine, 1979, pages 546-47 Apostle Bruce R. McConkie
Brigham Young: ‘’ l believe the Father came down from heaven, as the Apostles said he did, and begat the Savior of the World; for He is the Only Begotten of the Father which could not have been if the Father did not actually beget him in person’’. (Journal of Discourses Vol. 1 page 238) AND ‘’The birth of the Savior was as natural as are the births of our children ; it was the result of natural action. He partook of flesh and blood—was begotten of his Father, as we were of our fathers’’ (Journal of Discourses Vol. 8 page 115)
Physical relations between God and Mary has been clearly advocated in the Church by such authorities as Brigham Young [1], Orson Pratt [2], Heber C. Kimball [3], Joseph F. Smith, [4], Joseph Fielding Smith [5], James E. Talmage [6], Melvin J. Ballard [7], J. Reuben Clark [8], Bruce R. McConkie [9], and Ezra Taft Benson [10]. Mormons believe that Christ was literally the Son of God in the flesh, and he was conceived in a natural, physical way according to eternal law.
Heber C. Kimball “In relation to the way in which I look upon the works of God and his creatures, I will say that I was naturally begotten; so was my father, and also my Saviour Jesus Christ. According to the Scriptures, he is the first begotten of his father in the flesh, and there was nothing unnatural about it.” (Journal of Discourses, 8:211)
“Christ Not Begotten of Holy Ghost... Christ was begotten of God. He was not born without the aid of Man, and that Man was God!” (Doctrines of Salvation, Joseph Fielding Smith, 1954, 1:18).
Bruce McConkie “These name-titles all signify that our Lord is the only Son of the Father in the flesh. Each of the words is to be understood literally. Only means only; Begotten means begotten; and Son means son. Christ was begotten by an Immortal Father in the same way that mortal men are begotten by mortal fathers.” (Mormon Doctrine, 1979, pages 546-47)
There is nothing figurative about his paternity; he was begotten, conceived and born in the normal and natural course of events, for he is the Son of God, and that designation means what it says.” (Mormon Doctrine, 1966, p. 742)
“There is no need to spiritualize away the plain meaning of the scriptures. There is nothing figurative or hidden or beyond comprehension in our Lord’s coming into mortality. He is the Son of God in the same sense and way that we are the sons of mortal fathers. It is just that simple.” (The Promised Messiah: The First Coming of Christ, p. 468)
I believe you may be reading more into this than is actually there. But I would definitely be interested in hearing what the present day LDS church has to say about this. Certainly there must be some recent official edict or proclamation floating around which states that God had sex with Mary. Until I see that, I am willing to give them the benefit of doubt.