in-group vs out-group kinship terms

Japanese kinship vocabulary splits between humble in-group forms used for one's own family (兄, 姉, 母, 父) and respectful out-group forms used for someone else's family (お兄さん, お姉さん, お母さん, お父さん). Choosing the wrong register can sound either stiff or rude — the in-group/out-group distinction (uchi/soto) runs through the whole language but is especially visible here.