Here in verse 16, we have “their cries their howlings and lamentations”, whereas in verse 17 we get “their cries and their howlings and their mournings”. One wonders here in verse 16 if there isn’t a repeated their missing before lamentations or perhaps a missing and before their howlings. In support of repeating both and and their in such conjunctive structures (as in verse 17), we have this example from Mormon 2:12: “when I Mormon saw their lamentation and their mourning and their sorrowing before the Lord”.
Even so, we have already noted that the repeated and is not always found in long series of conjuncts (see, for instance, the discussion under Alma 43:47). So the phraseology in verse 16 without the and after cries is quite possible. Variation in the use of the repeated and is acceptable here in Ether 15:16–17.
As far as the nonrepeated their goes, we note that when lamentation is conjoined (as in verse 16 but not in verse 17), there is typically no repetition of the determiner unless it is the indefinite article a without an intervening adjective:
with the repeated indefinite article
without the repeated determiner
Thus we actually expect “their howlings and lamentations” in Ether 15:16. So there is no reason to emend the text in this passage.
Summary: Accept the reduced repetition in Ether 15:16 (“their cries their howlings and lamentations”), even though the following verse has a fuller form with increased repetition (“their cries and their howlings and their mournings”).