From your expanded question, it sounds as though your main issue isn't really sibi but the fact that you aren't correctly construing fratrem as the accusative subject of the infinitive in the indirect statement.
apud milites: prepositional phrase telling where the subject performs the main verbal idea
questus (= questus est): main verbal idea
(Nice timing! I just read this passage a week ago…)
This is from the opening to the War with Catiline.
Igitur de Catilinae conjuratione quam verissume potero paucis absolvam; nam id facinus inprimis ego memorabile existumo sceleris atque periculi novitate.
Therefore, I'll give a short summary of the conspiracy of Catiline, as truthfully as possible—...
You are right, it is Sanctae Romanae Ecclesiae. For consistency with the current text, you might want to use ligatures instead of separate letters for the diphthong ae: Sanctæ Romanæ Ecclesiæ.
FWIW, the technical name for the analogue of conjugation when applied to endings of nouns (i.e., when nouns change ending according to grammatical function) is ...
In the Czech Republic there are many diplomas issued in Latin (definitely the largest Charles University does so) and hence official translation services are available. The services do include translations into English and German, because that's what Czechs need the translations for, the Latin original is normally accepted here just fine.
Well, a search for "Vatican" and "Latin translator" put me on to this guy, Daniel Gallagher, who has left the priesthood and has joined the Classics faculty at Cornell,
"[a]fter eight years at the Vatican translating the pope’s messages –
sermons, letters, even tweets – into Latin ..."
You can read the rest of the article here.
Which is really just ...
The Colombian Ministry of External Relations can produce an official certificate that Colombia has no official translators between Latin and Spanish: https://www.traduccionesbogota.com/la-guia-definitiva-de-traducciones-en-bogota-colombia/
I found this service when I searched Google:
They specifically mention translating diplomas from Latin, and are a member of the American Translators Association. I don't know whether that carries much weight in and of itself, though, since I'm not familiar with that association. They also mention their translations are accepted world ...
I'm only an intermediate student of Latin, but I think I'll learn a lot by translating this. Here's what I came up with.
In the time since Pope Clement XIII permitted several Churches to celebrate the Feast in
honor of the Most Holy Heart of Jesus together with its Office and Mass, the
faithful peoples everywhere have felt themselves awakened by such ...