We do not learn of the meeting between Mosiah and Alma. There must have been one so that Mosiah would know that there was reason to have Alma preach to the people. Alma clearly impressed Mosiah, and Alma’s ideas will be seen in the events that lead to the reign of the judges.
Alma does not preach to the whole group, however. It appears that the basic meeting breaks up, and Alma travels to the different groups. It is probable that there were specific areas in Zarahemla where each separate group would reside. It would have been unusual for them to be very well integrated physically, particularly since we will see that there was an uneasy political and religious integration.
Specifically, Alma has the opportunity to speak with Limhi’s people. They were, of course, much the same people, with Alma having separated from them only recently.