The phrase “and also his people” is semantically conjoined with the preceding he (referring to Zerahemnah). On the other hand, the final with them completes the verb covenant. (There are 23 occurrences in the text of the verb covenant being completed by a with-phrase.) In other words, the meaning of this passage is ‘he and also his people would covenant with them’. A typical Hebraistic construction in the Book of Mormon is to shift a conjoined subject to the end of the predicate or after the verb phrase (as here in Alma 44:19). For further discussion of this syntactic construction, see the topic delayed conjoined subject under hebraisms in volume 3.
The 1830 typesetter understood the parenthetical nature of “and also his people”, so he placed commas around this conjoined noun phrase. Unfortunately, in the 1849 LDS edition, the second comma was accidentally dropped. For the 1920 LDS edition, the punctuation was made consistent by deleting the first comma as well. In order to prevent confusion, the commas (or perhaps dashes or parentheses) should be placed around “and also his people” in the LDS text (the RLDS text has maintained the 1830 commas).
Matt Empey (personal communication) has suggested one other possibility here: perhaps the them here is an error for him—that is, the subject he (referring to Zerahemnah) is conjoined with “and also his people with him”, meaning ‘and also all his people who were with him’. We already know that Oliver Cowdery sometimes had difficulty distinguishing between Joseph Smith’s unstressed him and them, both pronounced as /ßm/ in colloquial language (see the discussion under 1 Nephi 10:18–19). It is also possible that the verb covenant can occur without a with-phrase, but such usage is considerably less frequent than the 23 cases elsewhere in the text where the with- phrase is present. There are only four examples in the current text (but the original verb form in 2 Nephi 1:5 is actually consecrated rather than covenanted ). The three original examples are found in Alma 50–53:
So it is possible that in Alma 44:19 the with-phrase may not complete the verb covenant, but instead may modify his people.
There are 12 instances in the text where the word people is immediately followed by a prepositional phrase headed by with, but all these examples are adverbial phrases that modify the verb, as in “and Coriantumr had taken all the people with him” (Ether 14:15). In the following example, one could interpret the prepositional phrase as postmodifying the noun people, but the more reasonable interpretation is that the prepositional phrase is adverbial and modifies the verb behold:
But the usage is not redundant in Mormon 6:7, as it would be if we emended Alma 44:19 to read “and also his people with him”. Thus the suggested emendation (“and also his people with him”) would be quite unusual for the text in Alma 44:19, whereas the interpretation of with them as completing the verb covenant is expected even though the disjointed syntax is difficult to parse.
Summary: Restore in Alma 44:19 the parenthetical punctuation around “and also his people” to ensure that the prepositional phrase with them will be interpreted as an adverbial phrase completing the verb covenant.