Oliver Cowdery immediately corrected states to state by erasing the final s. His correction is undoubtedly based on the reading of the original manuscript. Elsewhere in the Book of Mormon, we have only the singular state, which is what we expect in English. In particular, there are four additional cases where carnal modifies state, and each is in the singular even though the context always refers to more than one person:
Summary: Retain the singular state in Mosiah 4:2, in accord with Oliver Cowdery’s immediate correction in 𝓟 and in agreement with usage elsewhere in the text.