Milne, who kicked four goals in the Saints' 46-point win over Gold Coast on Sunday, told teammates of his intention to retire on Saturday.
Coach Scott Watters confirmed Blake and Koschitzke, who is fighting to overcome a calf injury to play his 200th game, would also call time on their long careers.
"You couldn't get three better team men, and I can't speak highly enough of the way those players have helped mentor the younger players coming through," Watters said on Sunday.
"They're three very selfless individuals, and I just hope everybody comes out and gets right behind and acknowledges them in what will be their last games in our colours.
"One thing that we've been very focused on is allowing them to make really clear, calculate decisions on whether they feel they can go on."
Blake has played 218 games for St Kilda since making his debut in 2000, while Milne, who played his first game in 2001, will finish on 275 games.
Watters said Milne, who has kicked 572 career goals, sat comfortably alongside the game's great small forwards.
He said the 33-year-old's decision to retire was based on his ability to contribute next season, not his ongoing court case.
"What you don't see, and what the statistics don't actually show you, is the impact he has around the football club," Watters said.
"He is one of the players that actually make training a better place, and players love playing with him.
"He is an absolute team man and I take my hat off to the way he's gone about his footy at this club."
Veteran Saint Lenny Hayes, who confirmed on Sunday he would play on for a 16th season in 2014, said it would be an emotional build up to the last game of the season.
"They've been such great servants of the footy club, and we just want to send them off in the right way," he said.
"I think it's on every player that lines up with them next weekend, we have to show the same sort of courage and effort those three have shown over their careers.
"We're coming up against a very good side, and that's what we've loved doing – measuring ourselves against those top four teams."
While Milne and Blake appear certain to play farewell matches, Koschitzke, who has not played since round 14, will need to prove his fitness.
Watters said the club was doing everything it could to get the 30-year-old to his milestone game.
"I'm the easy one to get past, getting past our medical staff is pretty challenging at times," he said.
"As a club we would like him to get to 200 games. At the same time, we've got to make sure that every player who takes the field, there's a level of performance that's required.
"He's been close and he got good volume in this week. We just have to assess it as we go."