The text shows that most of the king-men were of high birth. They were aristocrats. They were landed people. None of the sons of Mosiah had wanted to be king twenty-five years earlier, but opinions may have differed among some of his nephews or people in the court of King Mosiah. When it says “of high birth,” there must have been some sort of bloodline involved. They may have been otherwise unknown descendants of King Mosiah the Elder, or of King Benjamin, or King Mosiah, or they could have been descendants of King Zarahemla, the last king of the Mulekites.
Note that they are called king-men. The Hebrew word for king is Melek. In Hebrew, there are no vowels, so Melek and Mulek look the same, just m-l-k. A Melek-man could be seen as either a Mulek-man or a king-man. There may be a play on words going on here. It is certainly possible that the Mulekites could have thought the Nephite experience was not going well from their point of view. If things were going well, the residents of Zarahemla seemed to be quite happy. But now, with the Zoramites opposed the Nephites, perhaps some of the Mulekites were wondering why they were getting caught in the middle of all this, saying, “Why do we have to go fight this Nephite battle? This is not our war.” We can understand politically how that could be their view. These Nephites, after all, moved in with King Mosiah 120 years ago, and they had been in charge a long time. Maybe some of them were thinking they ought to reassert their rights.
Book of Mormon Central, “Why Should Readers Pay Close Attention to the Mulekites? (Omni 1:19),” KnoWhy 434 (May 17, 2018).