In fact, we know from one source that the families were not only acquainted but also related. Elder Erastus Snow explained in a sermon delivered in May 1882:
“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.” (JD 23:184; italics added.)
That is to say, it appears that Ishmael's sons were already married to Lehi's daughters before the journey began.