For this passage, the first two RLDS editions (1874 and 1892) have “their own land” rather than the original “their own lands”. This change appears to be accidental since elsewhere in the text we have examples of both the plural “their own lands” (nine more times) and the singular “their own land” (five times), yet each of these other instances have remained invariant in number throughout the textual history. The 1908 RLDS edition restored the original plural lands here in Alma 16:8.
Summary: Retain in Alma 16:8 the perfectly acceptable plural lands in “to possess their own lands”, the earliest reading.