As discussed under 1 Nephi 17:14, the original text had quite a few cases of “arriving to a land” rather than “arriving in a land”. The editing tendency in the history of the text has been to replace these cases of to with in or at; here in Mosiah 24:25, the 1920 LDS edition made the change to in. The critical text will restore the original to in all cases where it is supported by the earliest textual sources, including here in Mosiah 24:25.
Summary: Maintain in Mosiah 24:25 the original preposition to (“they arrived to the land of Zarahemla”) rather than in.