And thus they departed into the wilderness with their numbers which they had , to go up to the land of Nephi, to preach the word of God unto the Lamanites.This is another example of an internally consistent reference. Compare with Mosiah 28:1
Now it came to pass that after the had done all these things, they took a small number with them and returned to their father, the king, and desired of him that he would grant unto them that they might, with these whom they had , go up to the land of that they might preach the things which they had heard, and that they might impart the word of God to their brethren, the LamanitesSo the Sons of Mosiah did not go on a mission alone. Later, we even learn some of their names. In Alma 21:11, we read about Muloki, Ammah and "his brethren".
Similarly, we tend to think of a group of 5 going around to destroy the church and being stopped by an angel: Alma + the 4 Sons of Mosiah. A careful reading of Mosiah 27:32, 34 suggests otherwise.
It seems that Book of Mormon authors often focus on certain people that are important for the narrative and leave out the rest. It may just be the custom or culture. Another example is Nephi mentioning his sisters once in passing in 2 Nephi 5:6. If he had not done that, many would be inclined to believe that he had no sisters.And now it came to pass that Alma began from this time forward to teach the people, and those who were with Alma at the time the angel appeared unto them...And four of them were the
This is one reason why I don't find it unlikely that the group who left Jerusalem was larger than we think. For instance that Lehi had a household with servants who came along. Or they encountered people on the way. Or they met and even mixed with other people after they arrived in America. But the Book of Mormon is just very focused on certain people that have a certain role to play in the way the history is related to achieve the real purpose of the book.