My only observation is that my father has been a huge influence on my taste in music. I started listening (seriously) to music quite late and thus I lacked a clear direction and defined taste. I think that fact made me very influenced by the thing played at home. Melodic power/prog metal, Neo-Prog, AOR (mainly Toto, late Kansas and Journey), Deep Purple and Rainbow was constantly playing, and my father was an active musician when he was younger, which perhaps was what I needed to pick up the bass guitar.
That passion for music was contagious and I still listen to a lot of those things he played. But I've never been passionate about anything but DP and Purple. I took those influences and developed them. I quickly knew more Kansas and Rush than my father did and constantly delved deeper into progressive territory, which represent my PERSONAL development and taste. I moved off in a tangent way, so to speak.
I do think that, at least for some of us, our parents' and siblings' tastes are important in building the musical ground you will have as an individual. But I've never experienced that rivalry you're talking about, James
. Only great fun in being able to enjoy things together and discuss it.