The 1830 edition accidentally dropped both here, but it was restored in the 1837 edition, undoubtedly by reference to the printer’s manuscript. Although 𝓞 was fully extant when Joseph Smith did his editing for the 1837 edition, there is no evidence that he ever referred to 𝓞 at that time. Currently, the original manuscript is not extant for this part of the text (for about three manuscript pages in 1 Nephi 13–15), including this part of the text.
Summary: Maintain both in “they both shall be established in one” since this is how the printer’s manuscript reads (here the earliest textual source).