The Sioux raised their children as prized possessions who were never abused or beaten. The extended family was important in the care of children and all members of the tribe were responsible for making sure children grew up safely.
Every one of your first cousins will have at least one and usually two grandparents who are not related to you. The English language does not have a term for this non-relationship. You can call them "my cousin's grandparents" if you need to refer to them.