The article often functions as a pronoun. (GGBB p211)
GGBB writes: The article is often used in the place of a third person personal pronoun in the nominative case. It is only used this way with the μὲν … δέ construction or with δέ alone. (Thus, ὁ μὲν … ὁ δέ or simply ὁ δέ.) These constructions occur frequently in the Gospels and Acts, almost never elsewhere.
Ὁ δὲ ἐγερθεὶς, παρέλαβεν τὸ παιδίον καὶ τὴν μητέρα αὐτοῦ νυκτὸς καὶ ἀνεχώρησεν εἰς Αἴγυπτον, (Matthew 2:14 )
The subject of παρέλαβεν is represented by the article here. But he, having risen, took the child…
Ἀσπάσασθε Φιλόλογον καὶ Ἰουλίαν, Νηρέα καὶ τὴν ἀδελφὴν αὐτοῦ, καὶ Ὀλυμπᾶν καὶ τοὺς σὺν αὐτοῖς πάντας ἁγίους. (Romans 16:15)
Here “all the saints” (πάντας ἁγίους) is modified by the relative clause where the article τους is functioning as the relative pronoun and the DMW. All the saints who are with them.
μετα τουτο κατεβη εις καφαρναουμ αυτος και η μητηρ αυτου και οι αδελφοι και οι μαθηται αυτου και εκει εμειναν ου πολλας ημερας. (John 2:12)
The article here should be translated “their”.