1 Nephi 7

After having returned with the brass plates of Laban, we read that the Lord told Lehi -

"...that it was not meet for him, Lehi, that he should take his family into the wilderness alone; but that his sons should take daughters to wife, that they might raise up seed unto the Lord in the land of promise.
2 And it came to pass that the Lord commanded him that I, Nephi, and my brethren, should again return unto the land of Jerusalem, and bring down Ishmael and his family into the wilderness."  (Book of Mormon | 1 Nephi 7:1 - 2)

In conjunction with this, I read some comments from David J. Ridges this morning concerning two quotes from Elder Erastus Snow -

“The Prophet Joseph informed us that the record of Lehi, was contained on the 116 pages that were first translated and subsequently stolen, and of which an abridgement is given us in the first Book of Nephi, which is the record of Nephi individually, he himself being of the lineage of Manasseh; but that Ishmael was of the lineage of Ephraim, and that his sons married into Lehi's family, and Lehi's sons married Ishmael's daughters.” (Journal of Discourses, 26 vols. London: Latter-day Saints’ Book Depot. 1854–86, 23: 184.)

And

"The Prophet Joseph informed us that Ishmael was of the lineage of Ephraim, and that his sons married into Lehi's family, and Lehi's sons married Ishmael's daughters, thus fulfilling the words of Jacob upon Ephraim and Manasseh in the 48th chapter of Genesis, which says: ‘And let my name be named on them, and the name of my fathers Abraham and Isaac; and let them grow into a multitude in the midst of the land.’ Thus these descendants of Manasseh and Ephraim grew together upon this American continent…” (Journal of Discourses. London: Latter-day Saints’ Book Depot. 1854–86, 23: 184).

This would suggest that Nephi had at least two older sisters that had married two sons of Ishmael.  This would tend to reflect that Lehi's family already had a relationship with Ishmael's family.