1- Child of uncle (father's brother) and of aunt (mother's sister) at the same time.
2- Child of uncle (mother's brother) and of aunt (father's sister) at the same time.
3- Someone who, in relation to others, has zero parents and four grandparents in common.
Double-cousin or double-1C:
1- Child of their parent’s full sibling with the other parent’s full sibling.
2- Person who, in relation to the other person, has zero parents and four grandparents in common.
My double-first-cousin is a good person.
Child of a person's maternal aunt (mother’s sister) with that same person's paternal uncle (father’s brother) or child of a person's paternal aunt (father’s sister) with that same person's maternal uncle (mother’s brother).
My double-first cousin is a good person.
Son of their maternal first cousin’s child with the paternal first cousin’s child or double-first cousin’s grandson.
My double-great-cousin-nephew is a good person.
Daughter of their maternal first cousin with the paternal first cousin or double-first cousin’s daughter.
My double-first cousin-niece is a good person.