𝓞 is not extant for the first part of this sentence; there is no room in the lacuna for of them except by supralinear insertion. One wonders, then, if perhaps 𝓞 actually read “and the remainder brake through and fled from us”, not “and the remainder of them brake through and fled from us” (the reading in 𝓟). Since the postmodifying of them is unnecessary, the most likely possibility is that in 𝓞 Oliver Cowdery initially omitted the prepositional phrase of them and supralinearly restored it later, perhaps when he read the text back to Joseph Smith. Elsewhere in the text, there are 12 instances of the noun phrase the remainder without any postmodifying of-phrase, while the remaining 44 instances of the noun phrase the remainder are of the form “the remainder of X”, of which seven read “the remainder of them”. (There is also one instance of the remainder part in the original text, in Alma 43:25.) For each case of the remainder, we will let the earliest extant sources determine the reading, thus “the remainder of them” here in Alma 57:33 (the reading in 𝓟). There is no explicit scribal evidence that Oliver Cowdery tended to omit the phrase of them in the manuscripts or, on the other hand, that he tended to emend the text by adding that phrase.
Summary: Maintain in Alma 57:33 the phrase “the remainder of them”, the earliest extant reading (in 𝓟); 𝓞 is not extant here, but apparently the postmodifying of them was supralinearly inserted in 𝓞.