Former Edinburgh fly-half Gregor Hunter and ex-Sale flanker Will Bordill have earned training contracts at Glasgow Warriors, along with George Hunter.
Gregor Hunter, 22, is currently recovering from a knee injury and is expected to be out for nine months.
He made 16 appearances for Edinburgh before being released last year.
Bordill, 21, and prop George Hunter, 22, have been aligned with club side Ayr this season, with the trio signing one-year deals.
"Unfortunately for Gregor he suffered a recurrence of a knee injury during our pre-season training and we're all really disappointed for Gregor that he's going to be spending some time on the sidelines," Warriors head coach Gregor Townsend explained.
"However, we will continue to support him through his rehab.
"We know George and Will very well. We are looking forward to seeing how they develop in our environment and also playing with their club side when they're not involved with us.
"We know them well and they will add to the depth of our squad and we expect them to work hard to earn a place in the team and potentially a full-time professional contract next season."