The Invincible

There are 4 crew members in total to save, Krauta, Koval, Marit and Gorsky.
You won't get the achievement until later after the 4th member, so read carefully.

Krauta
When at The Camp you will find Krauta in the far tent, this is when you get in contact with Novik who will be with you for the rest of the story. Novik will get you doing a few tasks inside the tent and then you can head out. When outside the tent Novik will try to make you find the other crew members but we don't want to do this, so go through the dialogue and when the option comes be sure to select 'I'm not leaving Krauta alone like this'. This will ensure we rescue Krauta as part of the achievement.

Koval
You will find Koval at the top of the excavation site still alive with pages of his notes all over him and after a bit of dialogue Novik will tell you to take him back to the lander which will secure his evacuation. Once we drop Koval off at the lander be sure to select 'I have to go back for Marit' otherwise there's no way to go back for her and ultimately this achievement will fail.

Marit
Marit is also located in the excavation site. If you selected the correct dialogue above when taking Koval back to the lander then you can now go back for Marit and bring her back to the lander to also secure her evacuation.

Gorsky
After reaching 'The City' you will now make our way through and find the final crew member number 4 Gorsky, here we will need to select the correct dialogue to ensure he is evacuated along with the others.

Proceed to pull Gorsky out of the ground and as you go through the dialogue select 'I have to get him oxygen first' then next select 'I'll give him mine' and click his oxygen pipe, then finally select 'Here you go Gorsky. [Give your oxygen]'.
It's up to you if you tell Novik and either way you will carry him away.

Continue the game and when you reach the crossroads be sure to take the Road to the Alliance Field Base
Finally when you reach the alliance field base for the first time head into the control room and collect the Alarm Print that's sticking out the machine next to the map. Go through all the dialogue and after finding out it's Gorskys ID number on the print this achievement should finally pop.

If you need more help with this you can follow my video guide below:

Here's my video guide: