Since the game is designed to play only once, if you want all achievements in a single playthrough, you may need this guide. Well, it is easy enough to get all of them in one run. I hope this guide serves you well, enjoy!

Take both paths to the house



This is the first achievement that you can get during the course. There are two roads to the Finch's House (you'll see something on the right one :D). Walk on one to the house and step back on the other 'til you see all the subtitles on the two roads, then you'll get this achievement.

Look in all peepholes and telescopes long enough to hear Edith's commentary



There are 9 peepholes and 1 telescope in this game. You need look in all of them to hear all Edith's commentaries to get this achievement. I'll show you their locations below according to the general story order. (It is noteworthy that you can use chapter replay option to get this achievement, and each peephole/telescope has only one dialogue)

Before you enter the Finch's House from the side door, there is a "peephole" on the fence. Look into it to hear Edith's dialogue. This one doesn't count as a peephole according to several comments down below, so I just want you to know that there is a peephole and you can hear Edith's words.

Once you have entered the Finch's House, 6 peepholes are available. 1 on the first floor, 5 on the second floor.
Follow the story, you will get out of the house and come to the family's cemetery. When you see Odin Finch's statue, go past him and turn right to where the telescope is. Zoom in to get a clear view of the Old House and hear Edith's commentary.

After you climb all the way to the upper area of Finch's house, you'll pass a small classroom and find Milton's castle (you can enter Milton's castle through the back window of it). Finish Milton's story and return, with Milton's castle on your back, you'll see Lewis' "psychedelic" boat at a higher position.

Catch 2 rabbits with only 2 swoops



When you play as Molly the Hungry Owl, catch 2 rabbits with 2 swoops. Catch one at a time. Swoop when you're close enough to the rabbit and navigate yourself carefully. If you failed to do that, quit the game and restart it. You'll start from the beginning of Molly's story.

IMPORTANT: You should only swoop 2 times! If you swoop 3 or more times, you will fail. If you need additional help, you can check the comment section to know how other players got this achievement.

Let the drunken sailor finish his song



When you play as Molly the Hungry Octopus/One-tentacle Monster, sneak to the central cabin of the ship, wait until the drunken sailor finishes his singing of "The Drunken Sailor" (it's kind of long I must say), then eat him.

Clear all balls off the pool table



When you play as Barbara the Comic Superstar, you'll get a crutch and walk into a basement room with a pool table. Just hit every billiards off the table to get this achievement. (If the achievement doesn't pop up, clear those cans, too!)

Knock all the letters of Gregory's name into the bathtub



When you play as Gregory the Bathtub King, make your frog charge and then jump. Knock down all the GREGORY name letters to get this achievement. This may be the hardest achievement to get in the game, but relax, as long as your frog doesn't knock that whale toy into the bathtub, you can try it forever. Just don't charge too much, or your frog will hit the bathtub wall and bounce too high. Good luck!

Finish all stories



Just finish all Finch's family stories. From what I remembered, the order of stories is:
Molly-Odin-Calvin-Barbara-Walter-Sam-Gregory-Gus-Milton-Lewis-Edie-Dawn-Edith.

See Johann's name in the ending credits



Watch the ending credits scene and wait until Johann appears, then you'll get this achievement.
He is the UNLOCKABLES PROGRAMMER, and he is an UNLOCKABLE PROGRAMMER.

Play Calvin's story again



After you finish the game, you'll be able to replay each chapter. Play Calvin's story again, then you'll get this achievement.

I'm not a native English speaker, so if there are any mistakes or questions, please let me know. Give a like, maybe? Anyway, I hope you love this game as much as I do, thanks!