Here the 1874 RLDS edition replaced the plural lands with the singular land, perhaps unintentionally. As discussed under 2 Nephi 9:2, either singular or plural is possible in this context. There are 13 other examples that use the plural lands in referring to one’s inheritance, including one more with the verb give: “and they did nourish them and did clothe them and did give unto them lands for their inheritance” (Alma 35:9). Here in Alma 43:12, the 1908 RLDS edition restored the original plural to the RLDS text.
Summary: Maintain in Alma 43:12 the original plural lands in the expression “lands for their inheritance”.