Here the 1840 edition accidentally omitted the repeated the for the conjunctive noun phrase “the Lamanites and the Nephites”. The 1908 RLDS edition restored the the to the RLDS text. As discussed under Enos 1:24, this conjunctive structure always has the repeated the. For general discussion, see under conjunctive repetition in volume 3.
Summary: Maintain the repeated the in “the Lamanites and the Nephites” in Alma 22:27 (and elsewhere in the text).