Brothers a Tale of Two Sons

During Chapter 6, once you have left the boat and make your way down the path a little you will notice a large turtle. From the turtle, go to the path on the right and you will see 3 baby turtles in the area, once of which is on the platform above where you need to give a lift to the younger brother to get him up the ladder, so he can slide the turtle down. Ater that interact with all three of the turtles to push them down the slide right at the back end of that area you're in, once all turtles are down the slide and in the water , the achievement will unlock.

Just after the part of Chapter 6 when you get off the boat you will see a large turtle. It's 3 children are in this area and lying stranded on their backs, use the two boys to pick them up and slide them down the ice slide back into the water where their mum is. The first two turtles you can't really miss, the 3rd one is over to the right side and you need to use the older brother to give the young brother a boost up and he can then push the 3rd one down so you can then both pick it up and take it to the ice slide. Once all 3 are back with mum head over to where mum turtle is and the achievement will pop.

This guide will walk you through all of the achievements in just 2 hours, timestamps are below the video


ACHIEVEMENTS LIST TIMESTAMPS
0:00 – Intro and Prologue
3:27 – Take a Break Achievement
10:37 – Chapter 1
10:57 – Wishing Well Achievement
14:39 – Love Birds Achievement (Part 1/2)
15:00 – Bunny Buddies & Black Sheep Achievements
24:14 – Chapter 2
42:45 – Chapter 3
44:06 – Falling Star Achievement
51:55 – Chapter 4
52:15 – A Sad Tune Achievement
58:00 – Windpipe Achievement
59:50 – Love Birds Achievement (Part 2/2)
1:14:03 – Chapter 5
1:18:00 – Call of the Giants Achievement
1:23:34 – Chapter 6
1:24:06 – Behind the Curtain Achievement
1:28:10 – Turtle Soup Achievement
1:30:45 – Whale Song Achievement
1:38:04 – Chapter 7
1:54:26 – Epilogue