Key back Aleer and winger Jacob Wehr have both told the Giants they want out of the club, following Saturday's heartbreaking defeat to Hawthorn in an elimination final.
Aleer is out of contract and has requested a trade to the Saints, where he is poised to take up a four-year deal.
It comes a year after St Kilda originally pitched to lure Aleer out of GWS, where he would be on a much less lucrative contract if he stayed.
The athletic 24-year-old, who was a first-round draft pick in 2021, played 13 AFL games this year after managing just 12 across his first three seasons.
Carlton free agents Tom De Koning and Jack Silvagni are also set to join St Kilda and could be joined by West Coast premiership forward Liam Ryan, who is keen to play under Ross Lyon.
Aleer and Silvagni are set to beef up the Saints' back-line alongside veteran Callum Wilkie and young star Alix Tauru.
St Kilda, who finished 12th and won just nine games this year, are also one of the clubs interested in Gold Coast midfielder Sam Flanders.
Wehr has played 39 games for GWS over four seasons and is tipped to join Port Adelaide as a free agent.
The 27-year-old qualifies as a delisted free agent after he was delisted by the Giants in 2024.
Elsewhere, 2021 first-round draft pick Campbell Chesser has reportedly told West Coast he wants a trade to Carlton.
Brodie Kemp will remain with the Blues on a new two-year contract, while Neil Erasmus has reportedly inked a fresh three-year deal with Fremantle.
Sydney have delisted former Essendon swingman Aaron Francis and Blake Leidler.
Francis, the No.6 draft pick in 2015, played 30 games over three seasons for the Swans after 54 with the Bombers.
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