Jesus called them.
In the boat
With the hired men.
They followed after Jesus.”
καὶ εὐθὺς ἐκάλεσεν αὐτούς· καὶ ἀφέντες τὸν πατέρα αὐτῶν Ζεβεδαῖον ἐν τῷ πλοίῳ μετὰ τῶν μισθωτῶν ἀπῆλθον ὀπίσω αὐτοῦ.
Once again, the similarity with Matthew, chapter 4:22, is quite striking, almost word for word. Then as Jesus had done with the other two brothers, he immediately called these two brothers (καὶ εὐθὺς ἐκάλεσεν αὐτούς). Just like Simon and Andrew had done, they left both their boat and also their father Zebedee (καὶ ἀφέντες τὸν πατέρα αὐτῶν Ζεβεδαῖον ἐν τῷ πλοίῳ). However, they left their father with some hired servants (μετὰ τῶν μισθωτῶν) that was not mentioned in Matthew. Both James and John, the sons of Zebedee, followed after Jesus (ἀπῆλθον ὀπίσω αὐτοῦ). So now, we have the first four disciples of Jesus, two sets of brothers, according to Matthew and Mark.