Here is the full list of all 22 We Were Here Together achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Assisted in disabling the tesla reactor
Split up and infiltrated the Cathedral
Discovered a way across the ravine
Discovered a way through the abandoned mine
Reached the top of the excavation site
Set out on a rescue mission
Invite a friend to play We Were Here Together
Split up and infiltrated the Tower
Disable the tesla reactor
Refilled the colored tanks
Get rescued from the watersilo
Rescue your partner from the watersilo
Exterminate the carnivorous weeds
Created the pesticide
Solve the puzzles of the High Alchemist
Solve the puzzles of the Head Priest
Create the Soulstone through the power of alchemy
Assist in creating the Soulstone
Solve the Guardians' riddle
End a part of yourself..
Sacrifice a part of yourself..