Hello! Sadly, I think you can't change this - to make a godchild, you have probably set your parents as the godchild's secondary parents which is everything the program really "counts" when calculating relationships. Adding "godparents" or "adoptive", "step" or "surrogate" parents is only a flavor thing for users, as far if I know.
If you find a solution though, it would be great if you could post an update!
