Brown was picked up by the Giants in 2018 as a Category B rookie, making the switch from Gaelic Football to Aussie Rules.
The Irishman provides versatility, being able to play in defence and up forward, shown in his fourth game, kicking four goals in the Round 16 win over Hawthorn.
The Bendigo product jumped into the club with a big splash, breaking the 2km time trial record in his first week.
At 18 years old, Hamilton looks to have a big future ahead of him and in his three games thus far has averaged 13.4 disposals and 3.7 tackles.
Wehr signs on after an impressive first season at senior level.
The running defender finally got his chance in 2020, when he was drafted at 24 years of age.
Since his debut, the Woodville-West Torrens export has played 10 straight games, also kicking four goals as a defender.
General Manager of Football Jason McCartney said the club is pleased to have locked in all three signatures.
"We’re really pleased to extend the contracts of Cooper, Jacob and Callum," he said.
"We have a great group of young talent coming through at the GIANTS, and these three guys have all shown what they can do when given the chance."
GWS will travel to face the Western Bulldogs on Saturday at Marvel Stadium at 1:45pm (AEST).