I can see why this is needed. English has very broad words for relatives like "grandfather" or "aunt". Most languages have more specific words, especially Chinese where there are separate words for fathers or mothers side, older or younger and sibling or siblings spouse. You also often use these relation words rather than their names when referring to a relatives. If this code was in Chinese, they would all be short…
In Vietnamese there are at least 4 different relationships that we call "uncle" (father's/mother's older/younger brother) in English! I have no idea how you refer to cousins. My teacher told me when he visits family he often doesn't know the word for his own relationships. Apple trying to capture a complete multilingual kinship lexicon sounds like an impossible task, I guess they must be focussing on specific languages here (Chinese is a good bet).