Here the subject thou was accidentally omitted in the 1837 edition. The resulting defective text was maintained in all subsequent editions until the 1908 edition for the RLDS text and the 1920 edition for the LDS text. Perhaps the lack of familiarity with the use of thou from Early Modern English made it difficult for 19th-century editors and typesetters to recognize an error here. The 1908 RLDS edition probably relied on 𝓟 to make the change, the 1920 LDS edition on the 1830 edition.
We should also note here the use of thou for the plural. There are a number of instances in the Book of Mormon where an original second person singular pronoun (thou, thee, thy, or thine) has been emended to the corresponding second person plural pronoun (ye, you, your, or yours). For some discussion of this editing, see under 1 Nephi 3:29 (or more generally under thou in volume 3). But not every instance of this original usage has been edited out of the text. We have this example here in Helaman 8:2. And Jacob 5:75 has a couple examples where the singular second person pronoun has never been emended to the plural: “he calleth up his servants and saith unto them … and thou beholdest that I have done according to my will ... and blessed art thou”.
Summary: Maintain in Helaman 8:2 the second person singular pronoun thou, even though it refers to more than one person; such usage can be found elsewhere in the original text.