unni(언니) = this is a term that koreans use when a younger female is calling an elder female. which is similar with english word(sister). but not between different generations.
Orabeoni(오라버니)= a term for younger female calling an elder male in same generation with respective manner.
Oppa(오빠)= same with above but not with respective manner. not considered rude. considered as friendly word for Orabeoni