It is from this verse that the composition of Ishmael's family can be determined. Ishmael and his wife had two sons and five daughters. When they left Jerusalem, the sons had already married (and possibly had children) as implied by the phrase, the two sons of Ishmael and their families. The five daughters, on the other hand, were all single. The math works out nicely. Each of Lehi's sons marry one of Ishmael's daughters, and Zoram marries the oldest daughter. Therefore, there are no unmatched members of the camp until Jacob and Joseph are born.
"Our tradition that Ishmael's ancestry went back to Ephraim, son of Joseph, is based on a discourse given by Elder Erastus Snow, in Logan, Utah, on May 6, 1882. He said, '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 abridgment 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.'
"From the above quotation and from 1 Nephi 7:6 we may propose that two of Ishmael's sons had married daughters of Lehi and Sariah. That would mean the two families were already related by marriage, which might explain Lehi's seeming nonchalance about instructing his sons to bring Ishmael's family down into the wilderness. There might already have been marriage plans between the two families—only the setting for the ceremonies would now have to change from the city to the desert. Another reason why Ishmael's family in particular was elected to join Lehi's was that Ishmael's had five unmarried daughters; the four sons of Lehi along with Zoram would in time marry Ishmael's daughters—a perfect five-way match set up in advance by the Lord." (Kent P. Jackson, ed., Studies in Scripture, Vol. 7: 1 Nephi to Alma 29, p. 30.)