My great times five uncle was Raleigh (Rolly) Robert Clack (1772-1842). His sister Catharine (Aunt Katy) Beulah Clack Rogers (1778-1850) married Rev. Elijah Rogers, (1774-1841) who were my great times four grandparents, and they all lived in Sevier County, TN in its early settlement stages.
This week was the first time I looked at Great Uncle Rolly's family at all. Maybe because it was so extensive! He had 16 children, with two different wives at different times. His first wife Mary Genieve Randles Clack (1770-1816) gave birth to 9 children. He remarried within the year of her death to Martha Kerr Clack (1787-1858) who then gave birth to 7 more children of his.
Someone* wrote a book about his family, and most of those children spread out moving west to Missouri and Texas. The book is Clack and Kindred Souls. It has some good genealogical research including this one page which clarifies the marriages of Clack and Kerr family members in Sevier County in the early 19th century. Without reading this page where the 4 Kerr/Clack marriages are laid out in simplicity, I would have just given up on understanding who was married to whom.
It is written with a bit of humor, which includes the various relationships of in-laws by having sisters and brothers of Great Uncle Rolly's wife marrying his older children.
I do wish I could find a document like this for many of the other families which married brothers/sisters etc.!! (That's a brother married a sister of the spouse of one person, not a brother married his sister!)
* Thanks to the authors of this book, Edna Clack Sacks and Joyce Kerr!