Brothers and sisters are siblings. Husbands and wives are spouses. Mothers and fathers are parents. Sons and daughters are children. Grandparents, grandchildren ... but what about uncles and aunts, or nieces and nephews?
In writing this, I scanned the "Similar Questions" sidebar and found that half of my question is already answered; there is no real term for nieces and nephews. Bummer. But I'm still wondering about aunts and uncles: does anyone know about that?