Here in Mormon 9:8 the text has been edited so that the initial he is consistently used throughout the passage. Joseph Smith, in his editing for the 1837 edition, twice changed they to he; the associated verbs were also changed in the 1837 edition to the third person singular, from have to has and do to does.
As explained under 1 Nephi 10:18–19, such switching in number for generic pronouns does occur in the original text. For another example like this one involving more than one pronoun, see under Alma 12:10–11. The critical text will restore the original plural usage to the second and third main clauses here in Mormon 9:8.
Summary: Restore in Mormon 9:8 the original reading with the generic plural forms they have and they do, even though the first main clause uses the generic singular he.