Here the 1837 edition omitted the universal quantifier all, probably accidentally (Joseph Smith did not mark the deletion in 𝓟). The 1908 RLDS edition restored the original all to the RLDS text, probably by reference to 𝓟. Since either reading works, the critical text will restore the all, the reading of the earliest sources. There is another example of all in the same prepositional phrase:
Note also in this second example the parallel use of all in the conjoined phrase, “nor even among all the house of Israel”.
Summary: Restore in Alma 49:8 the all before “the children of Lehi”, the reading of both manuscripts and the 1830 edition.