First cousin's great-great-grandson.
My great-great-great-cousin-nibling is a good person.
The grandchild-in-law of one's parent-in-law's sibling.
My co-cousin-nibling-in-law is a good person.
1- Nibling's spouse.
2- Spouse's nibling.
My nibling-in-law is a good person.
1. The child-in-law of one's sibling.
2. The child of one's spouse's sibling.
My nibling-in-law is a good person.