My husband David's paternal grandma was part of a sibling group of 12 children. Her father had two wives. Each wife had 6 babies. The first baby from the first wife and the last baby from the 2nd wife died in infancy.
David's maternal grandma was from a sibling group of 15 children. Her father also had two wives. He fathered 9 children with his legal wife and at least 6 with his 2nd wife. Wife #1 also became wife #3, but no more children came along between them. It was a marriage in name only.
My 2nd great-grandparents along my maternal grandfather's father line had 10 or 11 children.
A 3rd great-grandma, along through my maternal grandfather, had at least 8 children with her Vickery husband and 7 children with her Smith husband (my line). Her Smith husband was previously married and had 2 children with his first wife, who appears to have died in childbirth. Her Vickery husband died relatively young and doesn't appear to have had another wife. So, that makes at least 17 children, all related to me, but some not genetically related to each other.
There are many sibling groups of 9+ in my mother's family.
My patrilineal 2nd great-grandparents had 13 children, some of whom went on to have decent-sized families themselves. My great-grandparents along that line, however, only had one child. So, my grandfather, who had about 9 million first cousins had children who had no paternal 1st cousins.
