Child-in-law's father.
My co-father-in-law is a good person.
co-father-in-law.
Stepchild-in-law's father.
My step-co-father-in-law is a good person.
1- Stepchild-in-law's father. 2- Child-in-law's stepfather.
step-co-father-in-law.
Step-co-father-in-law.