Here is the full list of all 41 Hand In Hand achievements.
Start the game
Get the Invisible ability
Get the Strike ability
Start a co-op level
Help each other for the first time
Pass the gate with the timer
Pass the key through the portal
Provoke a rockfall
Complete the rope ride
Defeat the Slug
Find the twin monuments
Find the hidden stone
Steal the key from the Phantom
Hide from the Phantom
Jump on the invisible platforms
Open the doors using a beam
Complete the key puzzle
Complete the Phantom puzzle
Go through the thorny grove
Get on the elevators to the portal
Defeat the Phantom
Go throug the magical tunnels
Solve the dam puzzle
Solve the weight balance puzzle
Dodge the boulder
Assemble the beam generator
Exchange the keys in time
Complete the beam puzzle
Find a clue using a torch
Build a tower using boxes
Dispel the darkness with a beam of light
Find a way out of the maze
Defeat the Caster
Run through the dark tunnel together
Go through the darkness, follow the light
Defeat the Reaper
Finish the game
Find and take King Arthur's sword
Find out who lives in the green pipe
Find Georgie's boat
Find terminator like