Macdonald and Loiero have both signed three-year deals which will keep them in the Victorian capital until at least the end of the 2025 season, while Tom Eisenhuth has added a year to his time at the Storm.
Loiero has played 23 games since making his debut with the club in 2021, and was moving into the starting team through the middle of this year, playing consistent minutes otherwise off the bench, before a back injury put his season on ice.
With Kenneath Bromwich and Felise Kaufusi departing from the second row, Loiero will be in the mix for a starting spot next season alongside Chris Lewis, the arriving Tariq Sims and Joe Chan, and young gun Jack Howarth.
Macdonald, who was on a train and trial contract during 2022 after time with the Brisbane Tigers, moves into the club's top 30 for next season, and for the following two with a three-year deal.
He impressed during his 12 games, with his willingness to make tackles and do the hard yards in the middle third leaving him in and around the starting team.
Eisenhuth has been with the Storm since 2019, playing 40 matches for the club and is a valuable depth option in the forward pack, seeing his one-year contract extension confirmed.