Here it appears that Oliver Cowdery, when copying from the original manuscript to the printer’s manuscript, accidentally replaced their with the. In the original manuscript, the line ends with the, but there is clearly room at the beginning of the next line for the rest of the word (namely, -ir). Oliver frequently made errors trying to copy words at the end of the line (see the list of examples under Alma 11:21).
Here in Alma 13:10, the the was corrected to their in the 1837 edition, but this change was undoubtedly based on the obvious difficulty of the reading “on account of the exceeding faith and repentance” (there is no specific evidence that the original manuscript was ever consulted in the editing for the 1837 edition). Elsewhere in the text, whenever the text reads “the exceeding ” or “the exceeding ”, the noun is always postmodified by a relative clause or by a prepositional phrase headed by of:
Thus it is highly likely that in Alma 13:10 the original text (and probably 𝓞 itself ) read “on account of their exceeding faith and repentance”.
Spacing between fragments of 𝓞 also supports the existence of an additional their before repentance; in other words, 𝓞 may have read “on account of their exceeding faith and their repentance and their righteousness before God” (that is, with a repeated their before both the second and third nouns). But nearby in Alma 12:30, we have “according to their faith and repentance and their holy works”, which shows that “faith and repentance” can co-occur without repeating the their before repentance. Other conjuncts of “faith and repentance” show a lack of conjunctive repetition—specifically, they lack the repeated preposition:
Thus in Alma 13:10, it is probably best to follow the 1837 emended reading (with their before “exceeding faith and repentance”, but without any repeated their before repentance). It is also worth noting that Oliver Cowdery could have initially written their repentance in 𝓞 but ended up correcting the text by crossing out the their.
Summary: Accept in Alma 13:10 the 1837 emendation “their exceeding faith and repentance” as the probable reading of the original text.