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.
Create the Soulstone through the power of alchemy
Solve the puzzles of the High Alchemist
Exterminate the carnivorous weeds
Disable the tesla reactor
Split up and infiltrated the Cathedral
Solve the Guardians' riddle
End a part of yourself..
Get rescued from the watersilo
Invite a friend to play We Were Here Together
Created the pesticide
Solve the puzzles of the Head Priest
Assist in creating the Soulstone
Sacrifice a part of yourself..
Rescue your partner from the watersilo
Refilled the colored tanks
Assisted in disabling the tesla reactor
Split up and infiltrated the Tower
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