co-father vs godsib

co-father

noun
  • In a male homosexual couple, the nonbiological father (partner of the biological father) of a child. 

godsib

noun
  • One's sibling or kin via a godfamily tie: one's or one's child's godparent, or one's godchild's parent, or one's godparent's child. 

How often have the words co-father and godsib occurred in a corpus of books? (source: Google Ngram Viewer )