Tell Me Why

To get this one you need to choose all the bad options in the playthrough (ones that will give you the separating icon):

I had to do a full replay of ch3 to get this after my first playthrough was to get the strong bond

WARNING: There is a small chance that if you went with all "good" choices in previous chapters, you might have trouble meeting the requirements for this achievement (same goes for making bad choices and getting the Tyler ending). This, plus Tyler ending and both bond achievements, are extremely vague and this guide is going based on how I unlocked the achievement after 2.5 playthroughs of Chapter 3.

-Fail the panic attack app on your phone
-Don’t tell Eddy you were the one that killed your mom (this seems to be the other important factor)
-Tell Michael you are too different
-You can break open the chest or entered the code to the chest (Leo) - just don’t solve all the main (3) puzzles

And most important, Choose to keep your memory that Mary-Anne was going to kill you.

(It’s possible there are some extra steps in there, but I don’t want to take any away and have you not get the achievement and do another playthrough. Choosing the left memory and lying to Eddy seem to be most important though) These should get you the ending where Alyson is at the house at the end. Go into Mary-Anne’s old room (room on first floor next to the phone) and sit at the desk, then choose to finish the story.

Achievement pops after some dialogue.

Edit: Here is some extra info from StealFrmWork - "During my playthrough, I chose all the options to strengthen the twins’ bonds, passed the anxiety test, didn’t tell Eddie the truth, and originally accepted Tom’s version of events to get the ending with Tyler.

I restarted from “Veni, Vidi, Vecchi” (not in isolation mode) and sped through to making the decision again, this time choosing to keep the twins’ memory. This got my the Alyson ending."

Thank you Erinx212 for the help

Currently it is still unclear what exactly is needed but so far it turns out that you have to choose mostly negative, lie to Eddy in Chapter 3 and choose at the end Alyson's memory. I recommend to do this achievement together with the
on your second playthrough. You need 2 playthroughs to get all achievements.

There is no indicator in the game how many negative choices you needed, so for the safe side I recommend to replay! the game from chapter 1 (not isolated mode!) and be negative as possible. You can skip a lot of cutscenes and save a lot of time.

Here is a list of all my negative choices during my playthrough. The remaining choices should not be any effect to any achievement in the game (as example Tessa at Graveyard)

Chapter 1
Ferry
- I don't care
Ronan House - Puzzle Door
- Examine the door
- Open (door handle)
- Break down the door
Ronan House - Balcony
- Must be nice to forget
- Is something wrong
- That book changed everything
- Couldn't find the time
- Stop making it about you
Store
- Choose Alyson's memory
Store - Talk with Tessa (don't get any clues)
- We remembered details
- It's time to talk now
- April 2004
- You were mad she bailed on you
Police station
- Eddy did his best for me

Chapter 2
Ronan House - Outside
- Choose Alyson's memory
Car Stop (Telephone conversation with the realtor)
- Let's do it
Police station (After Archive Room)
- Are you kidding me?!
- She was struggling!
- So you called child services
- That's bullshit, Alyson!
- No, its not that easy
Store (After the plushie Battle)
- You're swell too
Graveyard - Totem
- Choose Tyler's memory
Ronan House - Docks
- Even after what I did for you?

Chapter 3
Eddy's House - Talk with Michael
- Don't tell Michael about the Memories
- Won't do any good
Police station
- I wanna forget
- I can't move on
Fishing with Michael
- We're too different
- I was the kid who killed his mom
Ronan House - Barn
- Break the Box with the crowbar and don't solve any puzzles
Ronan House - Dock
- Choose Alyson's memory (Marry-Ann threatened Tyler)

If you need a visual guide I have create a 100% video guide for this game with all achievements, all collectibles and all choices. The second playthrough / bad choices start at 35:32 (Timeline in spoilers)

Chapter 1

Chapter 2

Chapter 3

Second Playthrough

I have experimented a few times to get this achievement on different accounts. This achievement can be unlocked with either of the twin-related bond achievements. There are three dialogue options that affect this achievement.

1. You must not tell Michael about the memories.
2. Don't reveal to Chief Brown that Alyson killed Mary-Anne.
3. Stick with the Twins memory about how Mary-Anne wanted to kill Tyler.

If you do the first two but pick Tom's memory of Mary-Anne's death, you will get the epilogue that involves Tyler.

Hope this helps.

Philosophy:

Progression:

Chapter: Inheritance
Scene: Paternity Test (Restart progress from this scene)
Required choice: Do not tell Alyson's uncle the truth.

Chapter: Inheritance
Scene: Chosen Family (Updated progression from Scene, Paternity Test on)
Required choice: Directly respond to Michael with,

Chapter: Inheritance
Scene: Veni, Vidi, Vecchi (Updated progression from Scene, Paternity Test on)
Required choice: After Tyler says to Alyson, Whatever you choose - you got to live with it, you will control Alyson's response. Hold RT, aim left, and focus on, Stick to your memory, press A.

Chapter: Inheritance
Scene: Epilogue: A New Chapter (Updated progression from Scene, Paternity Test on)
Required choice: Complete story.