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