In the printer’s manuscript, Oliver Cowdery initially wrote “those of the fourth generation of your enemies”, then inserted “which shall live” after generation. The level of ink flow for the correction is unchanged, so the change appears to be virtually immediate. The resulting phrase is very awkward, and one wonders if the relative clause “which shall live” was inserted in the wrong place in 𝓟. One possibility is that the relative clause should have occurred after enemies:
Such an emendation avoids the commas that previous editors and typesetters have used in trying to help readers make sense of this passage.
Despite these arguments, there is clear evidence that the Book of Mormon text sometimes allows prepositional phrases to be displaced. For some discussion and examples, see under Mosiah 26:23; also see the many examples listed under displaced prepositional phrases in volume 3. In particular, there are a couple of examples involving the word generation where there is an intervening prepositional phrase or a delayed one that results in an unexpected word order:
To get a normal order in English for Mosiah 12:2, the prepositional phrase “because of their iniquities” should come either before “this generation” or after the prepositional phrase “into bondage”. In 3 Nephi 27:31, in standard English we expect something like “for I mean those of this generation who are now alive”. These awkward passages seem to imply that the original word order in Helaman 13:10 may very well be correct, despite its difficulty. The critical text will therefore maintain the unexpected word order: “and there shall be those of the fourth generation which shall live of your enemies to behold your utter destruction”.
Summary: Maintain in Helaman 13:10 the original awkward word order where “of your enemies” is separated from “those of the fourth generation” by the relative clause “which shall live”; displaced prepositional phrases are fairly frequent in the earliest text and will be maintained or restored, as the case may be, whenever they are supported by the earliest extant sources.