I take your point. If I include George as Technical Director of Miles Aircraft, who made the first flight of many of his brothers designs, then it would be churlish not to include the DeHavillands, where Geoffrey made the first flight of many of his father’s designs. I would be interested to know which, if any, aircraft met this criterion

Possilbly the most likely to replicate this would be Burt Rutan (Unless of course you know better)