According to Robert Matthews, we know from an earlier passage (1 Nephi 16:7) that Laman, Lemuel, Sam, Nephi, and Zoram had each married daughters of Ishmael. It is interesting that now, a decade or so later, each of them is said to have "his family" (2 Nephi 5:6), but Jacob and Joseph are referred to only in the singular, with no mention of a family. [Robert Matthews, "Jacob: Prophet, Theologian, Historian," in The Book of Mormon: Jacob through Words of Mormon, To Learn with Joy, p. 36]