Our first parents

When posting about Alma quoting Genesis, I noticed another difference between the texts. Genesis talks about Adam or 'man' being sent forth from the Garden of Eden. Alma talks about "our first parents" being sent forth from the Garden of Eden (Alma 42:2). The expression, "our first parents", is never used in the Bible but several times in the Book of Mormon when referring to Adam and Eve, see e.g. 1 Nephi 5:11, Helaman 6:26, 2 Nephi 2:15, Ether 8:25.

In Alma 12:21, a man named Antionah asks

What does the scripture mean, which saith that God placed cherubim and a flaming sword on the east of the garden of Eden, lest our first parents should enter and partake of the fruit of the tree of life, and live forever?

He must be quoting the brass plates. This could be a translation issue, but "our first parents" is quite different from Adam/man/mankind. So another more likely possibility, in my opinion, is that the brass plates had a slightly different wording than the Jewish Torah or a different passage referring to the event with this expression. That would explain the Nephites' frequent use of it.