Albert Barnes on Acts 10:23

And lodged them. They remained with him through the night. Four days were occupied before Peter met Cornelius at Caesarea. On the first, the angel appeared to Cornelius; on the second, the messengers arrived at Joppa, Acts 10:9; on the third, Peter returned with them, Acts 10:23; and on the fourth, they arrived at Caesarea, Acts 10:24,30.

And certain brethren. Some Christians. They were six in number, Acts 11:12. It was usual for the early Christians to accompany the apostles in their journeys. Rom 15:24, Acts 15:3, 3Jn 1:6, 1Cor 16:6,11. As this was an important event in the history of the church--the bearing of the gospel to a Gentile--it was more natural rant proper that Peter should be attended with others.

(c) "certain brethren" Acts 10:45