I think if we based the story from the drama only and from the episodes we had watched so far (Esp in ep 4) we can clearly see how considerate YJ is AGAIN toward his family.
When YJ checked on his tablet and SY came to offer coffee and started to show his over curiousity toward YJ secretary, we as the audience could see that he indeed tried to rub in his all seemingly nice forgiving kind of attitude and lending a hand to YJ as if he wanted to say “hey, I have forgiven you for your horrible act toward me so please you need to behave well and should be thankful that I didnt feel resentful toward you”
and like I said earlier, YJ recognised his older brother’s hidden message rightaway and responding with this question:
“for someone who was able to forgive me , why did it seem like that you rubbed it in too much?”
I personally liked this respond from YJ
but his brother seemed to be the one who always dwelled on the past and act selfishly. What he did toward YJ by seemingly talking nicely and etc etc its not an act of forgiving, rather he just wanted to make YJ to ALWAYS be aware of the past, to make YJ always FEEL BAD and to make sure YJ knows that YJ is the blaming party for what happens now —SY becoming a writer and not in charge of their company, because the kidnapping incident occured due to YJ abandoning him at the redevelopment area. (See ep 6)
and also, another scene which depicted how considerate YJ is also seen when SY hit him and at the last moment where YJ wanted to hit SY back, he refrained himself and instantly looked at his parents specifically his mother who cried because both of her sons fighting against each other. Basically YJ didnt want his parents to feel sad and hence he didnt fight back and chose to be silent and leave them.