think of it like you choosing how much of each skill you want to have when you start a game, Jaeui basically maxxed out his luck and intelligence, but it came with a catch, “Your Health is weak and dependent on your twin, your twin will also have horrible luck because you took it all!” so they are each others curses
Jaeui will stay alive as long as Taeui is alive yet will receive all bad omen to his body if Taeui is sick and wont recover until Taeui is. (Remember, Jaeui can be sick by himself bc hes weak)
and Taeui will have bad luck, yet in order for Taeui to have normal or good luck, his brother has to be sick, get bad luck, or die (essentially suffer)
so the curse and blessing is that one has to suffer for the other to thrive no matter what
(if smth is off please tell me! i finished the book a year ago and may be rusty)

I'm confused with the twin thing, can someone explain??