Meet the Kings and the Cronins.
The Kings are a New Zealand family. The father, Laurie King, was a captain with Cathay for many years, from the piston days right up to CV880s and possibly even 707s. His son (last time I heard) is a captain on 744s with CX; another son was on 747 Classics and yet another son was a 767 F/O with ANZ. (CX Flyboy might be able to update this).
The Cronin family, from Ireland, had strong links with Aer Lingus. Captain P Cronin was a captain with EI for many years, retiring with the 747; his daughter Grainne was the first ever EI woman pilot, now a 737 (possibly A320/321?) captain with EI and her husband was/is an Aer Lingus captain. Her sister was Ryanair's first woman captain.
There is a brother/brother combination in EI as well, although not sure if they have actually flown together. I'm sure they will at some stage.
However, Iberia has a family called Pombo, with about five or six family members in the same airline.