The singular whatsoever thing, the reading in 𝓞, was changed, probably accidentally, to the plural whatsoever things when Oliver Cowdery copied the text into 𝓟. The plural could have been prompted by the preceding plural nouns in the prepositional phrase “with stones and with clubs”. Interestingly, the 1852 LDS edition restored the singular whatsoever thing, but probably unintentionally. 𝓞 was definitely not the source for the change since at that time 𝓞 was still in the cornerstone of the Nauvoo House.
Elsewhere in the original text, there are 10 occurrences of “whatsoever thing” and 11 of “whatsoever things”, so either the singular or the plural is possible. For an example where Oliver Cowdery made the opposite change when he copied the text from 𝓞 into 𝓟 (that is, he changed an original whatsoever things to whatsoever thing), see under 1 Nephi 18:6. For all other cases of “whatsoever thing(s)”, the earliest textual sources agree with the current reading; in each case we let the earliest textual sources determine the reading. Therefore the singular whatsoever thing should be retained in Alma 57:14.
Summary: Maintain in Alma 57:14 the singular whatsoever thing, the reading of the original manuscript.