Here is the full list of all 12 Brothers - A Tale of Two Sons achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
You found a secret.
Make a wish.
You took a break from adventuring.
You re-united the two love birds.
You made the inventor dance.
You helped the turtles to the sea.
Every family's got one.
You made the bunnies play nice.
You threw someone's ball down a well… Shame on you.
You practised singing.
You sounded a giant horn.
You made someone feel better.