JOEL - Nephi was reporting something his father, the prophet Lehi said. As a prophet, Lehi could have such things revealed to him through revelation from God. Lehi also prophesied that Jesus would be born near Jerusalem(Alma 7:10) 600 years before it happened, and that the name of the person who would bring forth the Book of Mormon would be Joseph(2 Nephi 3).

TWIGGY - The Book of Mormon and the Book of Malachi:
The inclusion if an intrepetationary verse from KJV translators and erroneous verses:
Jesus quoted two chapters (3 and 4) from Malachi to the Nephites. These can be found at III Nephi 24 and 25. These two chapters are quoted almost verbatim from the King James Version, with very few alterations. III Nephi 24:5 omits the phrase 'from his right', which was added to the Isaiah text in italics by the King James translators. However, Smith was not consistent in removing the italicized inserts from the text. For example, III Nephi 24:10 retains the phrase 'that there shall not be room enough to receive it', even though seven of these words were interpretive additions to the text by the King James Translators.
Why the inclusion of this phrase when it wasn't part of the original words of Malachi and thus, could not have been the words said by Jesus?

JOEL - In the King James Bible, italics identify words that were necessary in English to complete the sense of a phrase but were not present in the Hebrew or Greek text of the manuscript. So italics does not necessarily mean that the phrase was not there, but that all the words needed to convey the message correctly into English were not all there. Bible translators supplied the appropriate missing words.
While Joseph Smith was translating the Plates he no doubt consulted the Bible at times when things were being quoted that were also found in the Bible. He may have been inspired to leave some things in(even the italicized words) if they were true ideas or if they helped to convey the intended meaning of the scripture, as I explained above. If he felt they changed the original meaning he left them out.

TWIGGY - The Book of Mormon- Jacob 5:
Confusion regarding olive trees and vineyards:
It is significant that the prophet Zenos appears to display some confusion about his metaphor. The parable of the vineyard begins with Israel as an olive tree located in a vineyard (Jacob 5:3). However, halfway through the narrative, the metaphor suddenly switches to the vineyard itself (Jacob 5:41). From this point on, the author repeatedly refers to 'the trees of the vineyard', apparently forgetting that the parable started out with olive trees as the primary metaphor, not grapevines.
Why the confusion when olives and grapes (grape vines) are utterly different?

JOEL - I see no confusion here. In this parable, olive trees representing the house of Israel, just happened to be planted in a vineyard, which represents the world. At no time in this parable does it speak of the grapevines in the vineyard, only about the olive trees planted in the vineyard. Whenever it speaks about the fruit coming from the vineyard it is talking about the fruit of the trees, which represents the good works that come from those within the house of Israel. The 'trees of the vineyard' are the olive trees. On the other hand, The vineyard spoken of in Mathew 21 is about the grapevines planted therin.