Here is an interesting example where Joseph Smith, in his editing for the 1837 edition, replaced they that with those who in the first relative clause, but then he left unedited the relative pronoun that in the following conjoined relative clause, probably because it wasn’t immediately preceded by a pronominal determiner like they (or those). Of course, mixed uses of the relative pronouns who, which, and that are not impossible, as in the following example:
Even though Joseph Smith edited the two instances of which to who in Mosiah 15:21, he did not change the first that to who but instead maintained the original mixture of the relative pronouns. For further discussion of the editing of the relative pronouns who, which, and that, see which in volume 3.
Summary: Restore the original use of “they that” in 2 Nephi 26:4; this reading is consistent with the repetition of the relative pronoun that in the following conjoined relative clause.