Hampster's Favorite

I’m thinking he’s faking the amnesia to try and restart his relationship with the uke. I also think it will be revealed later they are not truest related.

Edited to add:
I think he always wanted to be with the uke but because they are brothers it’s obviously frowned upon. He can stand up for the uke to the dad and defend him like he always wanted. Because he has amnesia and is going to inherit the business the dad will look the other way.