This achievement requires you to complete either of the three final missions "Something Sensible", "The Time's Come" or "The Third Way".
There is a video guide underneath the text guides if you prefer that instead.
In order to start the choice, become Franklin and head to his new safehouse. When you arrive and go inside your house, you will hear a knock at your door, answer it and you will get a cutscene. After it, you must decide the fates of your 2 friends, you can either kill Trevor ( Option A ), Michael ( Option B ), or neither of them ( Option C ). It is your choice but once you kill a character, you will never be able to access them forever in your save. Choose wisely.
Something Sensible ( Option A )
After you choose option a, you will have to go to start the mission as Franklin. When you start the mission, you will have a cutscene and after it, you have to chase Trevor. After a long chase, Michael smashes into Trevor's car and he hits an oil container. You will now have to shoot the leak of oil, but if you take too long, Michael does it for you and it kills Trevor. You then have a cutscene to end the mission.
Here is the video guide.
Credit for the video to GTA Series Videos (
https://www.youtube.com/c/GTASeriesVideos/featured )
The Time's Come ( Option B )
After you choose option b, you will have to go to start the mission as Franklin. When you start the mission, you will get a cutscene and after it, you have to chase Michael. You eventually stop and run after Michael along a construction site, until he has nowhere to go, and Franklin pushes him off but catches Michael's hand. If you try to save him, he tries to punch you, and he is dropped and if you take too long, he loses grip and falls. You then have a cutscene that ends the mission.
Here is the video guide.
Credit for the video to GTA Series Videos (
https://www.youtube.com/c/GTASeriesVideos/featured )
The Third Way ( Option C )
After you choose option c, you will have to go to start the mission as Franklin. When you start the mission, you will get a cutscene, after it, you have to go and pick up Lamar and go to the foundry with him. Once you go inside of the foundry, you will get a cutscene, and after it, you will get yourself in a big firefight. Take your time, cover as much as you can, switch between characters when you want a different position in the room, and be patient. Eventually, after taking care of all enemies, go to Lamar to help him. Once you help him, you have to take out the remaining attackers and helicopters, again, use the tips I gave you above. When the firefight is over, you will get a cutscene. After it, Franklin goes for Wei Cheng, Michael goes for Stretch ( Harold Joseph ) and Trevor goes for Steve Haines
FranklinOnce you arrive at the location, you should try to sticky bomb Wei Cheng's cars, if you fail to, then I recommend you to shoot their cars as they will stop when you continuously do, make sure that if you are doing this method, it is Wei Cheng's car that he is in or else you might lose him.
MichaelOnce you arrive at the location, you should try to shoot him at a further distance as there are Ballas that have guns that will start to shoot at you, take out the Ballas that remain left.
TrevorOnce you arrive at the location, you should snipe Steve Haines, once you do you will definitely get the cops on you no matter what, so escape them and you're done.
Once you have eliminated all three of them, you will be switched to Trevor where you have to go to Devin's house. When you arrive, there will be guards surrounding him, take each of them out, use cover, and be patient. Once each guard is taken out, go ahead and kidnap Devin. You need to then drive to the rendezvous point where a cutscene unfolds of all three of you, Franklin, Michael, and Trevor pushing the car with Devin inside into the sea in which it explodes, ending the mission.
Here is the video guide.
Credits for the video to GTA Series Videos (
https://www.youtube.com/channel/UCuWcjpKbIDAbZfHoru1toFg )