Glasgow Warriors hooker Brown joined the group in non-contact training last last week and is expected to take full part from today, with fellow Warrior and hooker Grant Stewart returning to the club.
Prop McCallum (22) last featured for Scotland on the 2018 summer tour and joins as fellow Edinburgh tightead Willem Nel continues his recovery from a calf strain sustained in the national team’s opening victory over Italy at BT Murrayfield Stadium on Saturday.
Blair Kinghorn claimed a hat-trick as Scotland dominated at Murrayfield, but the final score was 33-20 courtesy of Italy crossing three times in the final 10 minutes with Simon Berghan in the sin bin for the hosts.
While the visitors’ late flurry of points came with the match well beyond them, Laidlaw acknowledged Scotland cannot afford to be so sloppy when they face the reigning champions.
The scrum-half told BBC Sport: “Against a quality opposition like Ireland, you can’t release a Test match like that. We were well in control and we just gave Italy momentum by being less aggressive at the end and slipping off tackles.
“That will heighten our awareness for next weekend, against a quality team that’s coming here.”
Sign up to our mailing list here and we’ll keep you up to the minute with weekly updates from the world of rugby.