Many languages distinguish between inclusive and exclusive first-person plural pronouns (“we”). (Click or tap here to see more details)
The inclusive “we” specifically includes the addressee (“you and I and possibly others”), while the exclusive “we” specifically excludes the addressee (“he/she/they and I, but not you”). This grammatical distinction is called “clusivity.” While Semitic languages such as Hebrew or most Indo-European languages such as Greek or English do not make that distinction, translators of languages with that distinction have to make a choice every time they encounter “we” or a form thereof (in English: “we,” “our,” or “us”).
For this verse, translators typically select the inclusive form (including Paul and Philemon) for the equivalent of “our brother” and either the exclusive or inclusive form for “our dear friend.”
In Huautla Mazatec, the translators selected the inclusive we, in Tok Pisin, the exclusive form is used for the second occurrence (“our dear friend”).
Source: Velma Pickett and Florence Cowan in Notes on Translation January 1962, p. 1ff. and SIL International Translation Department (1999).