Family

Korean has two layers of family words: an intimate one, 엄마 and 아빠, learned as a child, and a respectful one, 어머니 and 아버지, used when the situation calls for distance or courtesy. Which you choose says as much about the setting as about the person. Koreans say 우리 가족 'our family' and 우리 엄마 'our mum' where English says 'my', because family is thought of as something shared rather than owned by one speaker; even an only child says 우리 엄마. Using 제 'my' is not wrong, but 우리 is what you will hear.

Two questions decide the word: is the sibling a brother or a sister, and is the person speaking a man or a woman? A man says 형 and 누나; a woman says 오빠 and 언니. The word follows the speaker, not the listener, so a woman telling a male friend about her brother still says 오빠. When you ask about someone else's family, take their point of view: ask a woman 오빠 있어요? and a man 형 있어요?. Older siblings get these titles, and are called by them instead of by name, because in Korean relationships the person above you in age is addressed by position.

The asymmetry is the point. Titles exist for the people above you, because those are the people you must address with care; people below you are addressed by name, so one word, 동생, covers them all. 남 and 여 are the Sino-Korean syllables for male and female, and you will see them again on toilet doors and forms. The neutral question 형제가 있어요? is useful precisely because you need to know nothing about the other person to ask it.