Yes, fratres is brothers, brethren. Fratres is the typical incipit for readings from the Epistles of St. Paul.NOTE: I think Fratres actually translates to both “brothers” and “brethren” in English.
I think the problem is that in American English, “brethren” isn’t as precise as it is in British English
From dictionary.com
brethren
plural noun
British Dictionary definitions for brethren
- **fellow members. **
- Archaic. brothers.
plural noun
- (archaic) a plural of brother
- fellow members of a religion, sect, society, etc