Political: Mosiah is the first named son in the list of sons given in verse 2. That primacy of position and the confirmation of the calling of Mosiah as the next king allows us to assume that Mosiah is the first born son of Benjamin. While we have no such information about Benjamin, from this example we may also presume backwards to Mosiah I. With the establishment of the new dynasty, Mosiah I kept the general lineal principles of kingship. The throne should pass from father to first son. Since this is very standard mode of transferring power, we may be confident that it is accurate for the Nephites at this point in time.
It may be important that at this point in the history of Zarahemla Benjamin finds that he must make a distinction between the people of Zarahemla and the people of Mosiah. It would be very natural that the two groups would keep their own kin groups separate, but these designations do not indicate kinship but political allegiance. The people of Zarahemla retain the name of their last ruler, who is surely passed on by this time. The lineal "Nephites: are designated by the term "people of Mosiah." This must refer to Mosiah I, as Benjamin has not yet appointed Mosiah II as his successor.
Once again we are required to read between the lines of the text. Benjamin has had controversy and conflict during his reign, though at this very point in time he as peace (verse 1). Even at this date (comprising the end of the life of Mosiah I and most of Benjamin's life - perhaps at least 60 years given the typical life span in the Book of Mormon and the overlap between Mosiah I and Benjamin) we have two identifiable political factions, one retaining the identity of Zarahemla and one the identity of Mosiah (and interestingly not Nephi). This division in the people becomes the background against which Benjamin's coming proclamation will make sense (see verse 11), and potential (or past) divisions between the two groups may also explain the need to declare Mosiah II as king "from mine own mouth." The clear pronouncement in a public forum would be calculated to decrease potential divisions and disagreements about succession.
Editorial: Mormon has skipped from one embedded speech to another. The interstitial text is descriptive of the situation, and the speech is allowed to stand on its own. So far in Mosiah the best information we may deduce about the nature of the original plates of Nephi is that in style they tend to the first person.. Of course this fairly logical for speeches, but we must remember that speeches had to be recorded, and it is not likely that we have them precisely as given. It is more likely that the first person nature of the plates of Nephi reflect the importance of the focal character, the king. Speeches and other discourses are given in the first person, reflecting very much the original, but very likely containing some differences due to later redaction and possibly editing.
Actual recorded speech is never as smooth as the written (excepting where authors attempt to write the oral forms). Thus when we find these clean first person discourses, we may know that the plates of Nephi are being cited, but should be cautious in presuming that we have the word for word speech of any of the speakers.