Cousins are a kinship in the family. They are their father's brother or brother's children, and they don't necessarily have grandparents. If grandpa has a brother, his brother's grandson is also his cousin.
Cousins are brothers and sisters other than the father's brother or brother's children, including aunts, uncles and aunts, that is, the children of aunts, uncles and aunts.
Blood relationship can be divided into direct blood relatives and collateral blood relatives. Lineal blood relatives are relatives who have a direct relationship, that is, people who have given birth to themselves and their descendants. Both parents are included.