Have you tried to search for it in it's kanji form? 従兄さん - someone else's MALE cousin 従妹さん - someone else's FEMALE cousin (従 + sibling kanji) + san/sama/chan/noting/etc...
If you were to teach someone kana, but focused on pronunciation... do you think it would be reasonable to start in this order? あいうえお、’えい’、’おう’、やゆよ、かくけこ、ききゃきゅきょ