Nobody understands the difference between 1st and 2nd cousins – or once or twice removed. I think it’s simple, actually, if you think about it as a ladder (above).
Point 1) It all starts with a pair of siblings (at top)
Point 2) It ladders down by generations. Going across a rung in the ladder equates to Nth cousins. Then moving up equates to Nth removed.
Examples:
- The children of siblings are first cousins
- The grandchildren of siblings are second cousins. (i.e., being second cousins means your grandparents are siblings.)
- The great grandchildren of siblings are third cousins. (i.e., being third cousins means your great grandparents are siblings.)
- Blue child and orange grandchild are first cousins, once removed.
- Blue child and orange great grandchild are first cousins, twice removed.