- Siblings have a common set of parents
- First cousins have a common set of grandparents
- Second cousins have a common set of great-grandparents
"X times removed" is the number of generations off you are.
So, my first cousin and I share grandparents. Her sons and I share common ancestors, but they're skewed by one generation (my grandparents are their great-grandparents).
So we are first cousins once removed.And then I tried to get into the advanced forms, and decided it would be easier to do a drawing, which is what I always do in person.
Click to make it larger if that's helpful.
Alice and Bob are married; their children, Cathy and Eric, married Dean and Fern, respectively.
So Henry and Karen are first cousins. Got it?
Henry would therefore be first cousin once removed to Nancy's son Ted.
Henry's daughter Ophelia is second cousin to Ted (same generation, share great-grandparents Alice and Bob).
Even more advanced:
If, in the picture above, George and Jerry are siblings to each other, Penny and Quincy are double first cousins.