If one thing is usually consistent in Star Wars, it's lineage/family descendants/etc., mostly due to the force ability implication.
eh, all that was retconned into it. Leia wasn't his sister until
ROTJ. Vader wasn't the father until
ESB. people still make fun of the Luke-Leia kiss at the start of that film. when the first
Star Wars released, and for several years after, Vader and Anakin were separate people, in fact they appeared as such in an early draft of
ESB. Obi Wan himself has to explain away the Vader retcon in one of the lamest scenes of
ROTJ. not so consistent. Leia being Luke's sister was a last minute patch to cover up Yoda's "There is another" which was originally going to be followed up in Lucas's ST. IMO family lineage was not really the main driving force behind the OT, and only barely for the PT.