Who are Nephi's sisters?

2 Nephi 5:6

6 Wherefore, it came to pass that I, Nephi, did take my family, and also Zoram and his family, and Sam, mine elder brother and his family, and Jacob and Joseph, my younger brethren, and also my sisters, and all those who would go with me. And all those who would go with me were those who believed in the warnings and the revelations of God; wherefore, they did hearken unto my words.

Who are Nephi's sisters?

We don't know how much information about these "sisters" was provided in the Large Plates of Nephi, because the 116 pages of manuscript that Joseph Smith had completed for the translation of the Book of Mormon were lost.  All the information we have about Nephi's family members comes from the Small Plates of Nephi, which replaced the lost pages of manuscript.

Nephi begins his record on the Small Plates with the following:  An account of Lehi and his wife Sariah, and his four sons, being called, (beginning at the eldest) Laman, Lemuel, Sam, and Nephi. 

Nephi tells about Lehi sending the 4 boys back to Jerusalem to persuade Ishmael to bring his family into the wilderness and travel with them to the Promised Land so the 4 sons could have wives to marry -- he says nothing about getting husbands for any daughters to marry.  Ishmael does indeed have 5 daughters, and also two sons, who are already married when they leave Jerusalem with Nephi and his brothers.  1 Nephi 7:6 6 And it came to pass that as we journeyed in the wilderness, behold Laman and Lemuel, and two of the daughters of Ishmael, and the two sons of Ishmael and their families, did rebel against us; yea, against me, Nephi, and Sam, and their father, Ishmael, and his wife, and his three other daughters.

Were Ishmael's sons married to Lehi's daughters?  Is that why Ishmael's family was singled out to accompany Lehi's family to the Promised Land?  

In 1 Nephi 8, when Lehi sees the Vision of the Tree of Life, he specifically mentions his wife, Sariah, Laman, Lemuel, Sam and Nephi -- but no sisters are mentioned.  This is telling because Lehi's concern was for the welfare of his family (Jacob and Joseph had not yet been born).  Some Book of Mormon scholars believe no mention is made of the sisters because the scriptures typically just talk about the men, but this Vision is very important to Lehi as it defines the eternal paths his family members will take.  It's hard for me to believe that he just didn't mention his daughters because he didn't think they were important enough.  Ishmael's family isn't mentioned at all in the Vision, suggesting that the two sons of Ishmael were not married to Lehi's daughters.

In 1 Nephi 18 when, just as Nephi's family are boarding the ship to cross the ocean, Nephi tells us that two more sons were born to the family:  7 And now, my father had begat two sons in the wilderness; the elder was called Jacob and the younger Joseph.  No mention of any daughters born into the family.
When Lehi blesses his children before his death, he also blessed "my sons who are the sons of Ishmael," suggesting a familial relationship, which would be if his two daughters married the two sons of Ishmael.  Or, he could have done so considering them his sons because he was the patriarch of the entire group.

So who are Nephi's sisters?  I do not think they are Nephi's blood sisters who were still single, because there were too many opportunities for Nephi to mention them.  I think they were either his sisters that were married to the sons of Ishmael, or his sisters-in-law that were married to Laman and Lemuel.

If so, then some families broke up when Nephi's group parted company with the Lamanites.  That may better explain the eternal hatred the Lamanites had for the Nephites, not just that the Nephites took the Plates of Brass with them or that Nephi was given the leadership position by the Lord.  Their hatred was because some of their wives followed Nephi instead of staying with them, and took some of their children with them.