The quartet depart the club after a combined 98 senior appearances in a purple and white guernsey.
Having been selected as a mature age draftee ahead of the 2019 season, the former Williamstown midfielder Bewley managed 25 games in his time with the Dockers, but struggled to create a spot in the senior side this season, having ended the 2021 season with just six appearances to his name.
Both Giro and Watson ran out on 14 occasions for the Western Australian team, but like Bewley failed to cement a place in Justin Longmuir's starting 22 across the past 23 Rounds.
As the most experienced of the group, Duman will end his time at Cockburn after completing a career of 45 games for the club.
Category B rookie Leno Thomas was also told that his services were no longer required by the club.
Despite alerting the group that their futures lay elsewhere, Fremantle's General Manager Peter Bell claimed that it had not been an easy message to deliver.
“This is always a really difficult time of the year to have to make these decisions,” Bell said in a statement issued by the club.
“I’d like to acknowledge the contributions of Brett, Taylin, Stefan and Tobe to Fremantle.
“They are players of great character, and it will be sad to see them leave the Club."
Bell also stated that with the Dockers' WAFL affiliate Peel Thunder still remaining in premiership contention this season, the group's days in boots out west may not be completely over.
"A decision will be made later in the week as to each players availability for selection at Peel, for the remaining two fixtures," he said in finality.
The Dockers will enter the off-season with seven places available on their list for 2022 after earlier parting company with Reece Conca, the retirement of club champion Stephen Hill and the impending departure of Adam Cerra.