I think I got it nailed. Jisu, Minsu, Hyeonsu & Shinae are first cousins. Jisu's dad(dead Guy), Minsu & Hyeonsu's dad(Coma Doc) & Shinae's Mom(Screeching Aunt) are brothers and sister. Jisu is a half sister to Sumi & Juho- all 3 having Wimpy as Mom. Suin is a half sister to Sumi & Juho -all 3 have the same Dad. Jisu and Suin are not blood related-Jisu's Mom is the second wife of Suin's Dad. Juho & Shinae are not blood related-Their Moms are ex-SIL. Minsu & Hyeonsu are full brothers. Sumi & Juho are full bro & sis. I hope in the last 30 eps they do not throw in a long lost sib because this all makes my hair hurt.
I don't see how Sumi can improve. Maybe she'll get sick and Jisu will be the only match so she can live. Nah, that wouldn't work. Sumi wouldn't be grateful anyway, the little brat. I hope nothing happens to their mother just so the daughters can develop a relationship. That poor mother has had a tough life.