First, you disable Steam Cloud synchronization for Prey.

Here are the save files for you to get the achievements:
https://drive.google.com/open?id=1vkKlRZB1O3SlgsEet6Fx8B6GKqjhXn0X

Remember to backup your own save files, before you replace it with this.

You can find your save files located at:
C:\Users\<Your Profile or Name>\Saved Games\Arkane Studios\Prey\SaveGames\

"I And It", along with "Awkward Ride Home" (which you can also get here) seem to be the two hardest achievements to get in the Prey base game, according to the global achievement stats.

Load up the "Arboretum" save file.

Then, all you need to do is to open Alex Yu's bunker door, kill him and you should get the achievement right after that. He'll be the 42nd and last Human to die. For those wondering, you don't need to bother about Danielle Sho.

You can get the "Awkward Ride Home" & "No Needles" achievements with the "Shuttle Bay" save file. Or if you have done only one of Human powered or Typhon powered playthrough, you can get the "Split Affinity" achievement as well by using neuromods and adding one other power which you have not tried and finish the game, then load it up again for "No Needles".

Load up the "Shuttle Bay" save file.

Then, run towards the shuttle, open the shuttle door and sit right next to Dahl for an awkward ride home. Yeah, just the two of you.