The reader might be confused over the meaning of “if ye have choice”. It doesn’t seem reasonable to interpret the subordinate clause literally. Nephi isn’t really asking whether Laman and Lemuel and the others have a choice. They apparently have their agency and could return if they wanted to. One possible way to interpret the conditional clause would be to replace the if with since (“and now since ye have choice / go up to the land”). A more plausible equivalence in modern English would be to replace have choice with the verb choose: “and now if ye choose / go up to the land”. In other words, the meaning is something like ‘and now if you wish / go up to the land’.
Summary: The expression “if ye have choice” is apparently idiomatic and is equivalent to the modern English “if you choose”, meaning ‘if you wish’.