We say '따님(daughter)/아드님(son), etc을/를 잃으니 얼마나 슬프시겠어요." or "어머님(mother), 아버님(father)를 잃으신데 대해 저도 유감입니다." at one's funeral. I know some people say words like "삼가 조의를 표합니다.", but it's too artificially stilted.