As already noted, the original text of the Book of Mormon has numerous examples of the -(e)th inflectional ending occurring with a third person plural subject. Here we have an example of doth where standard biblical style requires do since the antecedent of the relative pronoun which is plural (“the temptations and the sins”). The 1920 LDS edition made the grammatical change, but the RLDS text has retained the original doth. For further discussion and other examples, see infl al endings in volume 3.
Summary: Restore the original doth in 2 Nephi 4:18; even though the antecedent of which is plural, the original text has many examples of plural subjects taking verbs with the -(e)th ending.