Responses
His wife, teacher (Chae Rok), youngest son (Sung Kwan) and the other young ballerina at the studio (Sung Ah Yoon) are the ones who knows that gramps has dementia. The bully with thre red jacket (Sung Chul Kang) too I think knows? But idk
I don't remember which character knows grandpa's secret. I think the eldest son doesn't know it, if he does he would have prohibited him to go anywhere.
Anyway this is surely one of the best SLICE OF LIFE story I have ever read. I just hope the translation release is more frequent, I don't want to look the raws. Anyway thanks to everyone who translate this masterpiece. And thanks to the author.