The 1874 RLDS edition changed the order of “they all did begin” to “they did all begin”. The placement of the all between the helping verb did and the main verb is characteristic of the Book of Mormon text:
There are no other examples like Helaman 5:42 where the all comes before the helping verb form did and its main verb. But for other helping verbs, we can occasionally find examples where the all precedes the entire verb phrase, the helping verb(s) as well as the main verb:
The critical text will therefore follow the less frequent word order in Helaman 5:42, with the all before did begin.
Summary: Accept in Helaman 5:42 the original placement of all before the helping verb did: “they all did begin to cry unto the voice of him which had shook the earth”.