finaly! i thought serebii never let me in. anyway here it is, this is what did the trick for me, i suggest you to follow it carefully:
This trophy is somewhat really tricky to get. I just tried it 3 seconds ago and got it. This is what I did. I started a new game and saved it in the 2nd save file since I already beat the game. Then I just did what Ethan is supposed to do. This is what I did.
I shaved, took a shower, got dressed, went downstairs, completed the drawing. After I completed the drawing, I went to drink a cup of coffee and then drank some Orange juice and then went outside and laid/waited until Grace and the kids got home.
After they arrived, I helped Grace with the groceries, set the table perfectly and then went to talk to Grace. Not sure if you have to do that but I did. Once that was done, I went outside, swung Jason around and then picked up Shaun and ran around until it automatically stopped me. After that, you pick them up to show your strength. Then I did the sword fight, got some hits in, and let Jason defeat me. I did the rest of the prologue all the way to the “Sleezy Place” chapter load and got the trophy. Hope this helps.