Brothers in F1
Gary Brabham & David Brabham
Ernesto Brambilla & Vittorio Brambilla
Jose Dolhem & Didier Pironi (half brothers)
Teo Fabi & Corrado Fabi
Wilson Fittipaldi & Emerson Fittipaldi
Pedro Rodriguez & Ricardo Rodriguez
Ian Scheckter & Jody Scheckter
Michael Schumacher & Ralf Schumacher
Jimmy Stewart & Jackie Stewart
Gilles Villeneuve & Jacques Villeneuve Sr
Manfred Winkelhock & Jo Winkelhock
Peter Whitehead & Graham Whitehead
I got this list from the May 2001 issue of F1 Magazine.