I am not good at english, so I am not sure if I can answer
I explain you as much as I know.
mother 어머니 (Usually, you can talk "mom" 엄마)
father 아버지 (Usually, you can talk "dad" 아빠)
grand mother 할머니
grand father 할아버지
one's maternal grandmother 외할머니
one's maternal grandfather 외할아버지
aunt 이모, 고모
one's father's elder brother 큰아버지
one's father's younger brother 작은아버지
the wife of one's father's elder brother. 큰어머니
niece 여조카
nephew 남조카
(These expressions are same in Korea, but just differeny of sex)
sister 여동생
brother 남동생
(These expressions are same in Korea, but just differeny of sex)
Actually, In Korean culture, There are numerous expression that you adress someone elses family member
So I can't teach you all of the things but I wirte some expression.
If you want to learn Korean more, just contatc me