Grant Hardy (personal communication, 4 June 2007) suggests that the of after neither could be an error for on —in other words, they should not lay their hands on the sons of king Mosiah “nor neither on their brethren” (that is, on their fellow missionaries).
There is little evidence from scribal errors to support the replacement of an original on with of here in Alma 23:1. There are a couple of cases where on has been replaced by of with respect to the phrase “on the Yth month”:
In modern English we expect “the Xth day of the Yth month”, not “the Xth day on the Yth month”; thus the motivation for the replacement of on with of in these two cases is totally different than here in Alma 23:1 (if such a change actually occurred in the early transmission of the text).
If the original text in Alma 23:1 read “on their brethren”, I would expect it to read with only a single conjoined negative: or, nor, or neither:
In fact, Alma 23:1 is the only instance of nor neither in the text (or of nor either, the current reading in this passage), which implies a uniqueness of expression.
Ultimately, there is no problem here in Alma 23:1 since neither is acting as an equivalent to the word none (or any in standard English), for which the of is expected, as if the original text read “nor none of their brethren”. For the use of neither as a pronoun with the meaning ‘not any one (of more than two)’, see definition 2c under section B for the word neither in the Oxford English Dictionary.
Summary: Maintain in Alma 23:1 the preposition of before their brethren (“nor neither of their brethren”), the reading of the earliest text; the expression works here since neither is acting as equivalent to none, and there is nothing wrong with the phrase “nor none of their brethren” (except, of course, for the double negative in standard English).
Alma 24:15, page 2108, line 18
The 1905 LDS edition replaced the singular “his word” with the plural “his words”; in other words, an s needs to be added to the second “his word” in this sentence.
Alma 26:5, page 2137, line 22
The definite article the needs to be placed before the word passage, thus “the rest of the passage refers to the missionary harvest in the past tense”.
Alma 27:3, page 2157, line –9
The word war at the end of the line should be in the singular, not the plural (thus “weapons of war” rather than “weapons of wars”).
Alma 27:20, page 2168, line 9
The name Alma at the end of the line (since it is conjectured to have occurred there in 𝓞) needs to be set in all caps, thus ALMA.
Alma 27:22–24, page 2171, line 17
As explained under 3 Nephi 3:23 in part 5, the original text for the third line apparently had betwixt rather than between; thus the line here should be changed to read as “yea to the line which was betwixt the land Bountiful and the land Desolation”.