Don,
I knew about 6 trips but your post prompted me to look further and now I know about 10. I have a signed copy on Fonger's book that was a gift and an unsigned one I purchased.
www.earthrounders.com keeps a list . It is not always complete but a very good start. Note that Twins is one list and Air Races is a second list.
1971 Patricio Milmo and Jesus Delgado
1987 Don Fonger and son Jim Fonger
1987 Tal Talibi and Ken Bamford
1991 RJ Plimpton
1992 Dick Levin & Dan Boone
1992 World Race Gérard & Christiane
1992 World Race Marion Jayne and daughter Nancy Palozola, 2nd
1994 World Race Marion Jayne and daughter Patricia Jayne Keefer, FAI Gold Medal
2001 London-Sydney Air Race Denise Water and various copilots or none
2002 Cpt. Dick Sollner & Cpt. Bill Moore