My family (which includes siblings, cousins, parents, aunt's, uncles, grandparents) are all Eagles supporters and we would get together to watch games. I hated football, i think this is to do with tooo much of it at a young age eg. bothers footy matches, watching every eagles game, having to listen to it on the radio in long car trips - it really made me hate it.
BUT for the 2004 derby (i was 10) we were allowed to wear our teams colours to school, i made the decision it would be the Eagles. I only knew of Eagles and Freo and I didn't want to support team who wears purple as i thought the guys wouldn't take me seriously. That night I raced out to buy a wce scarf.... Eagle ever since
My brother was just like you, he supportered both the eagles but moreso the kangaroos in the early 90's even has a blue and white knitted blanket to show for it. But now after changing from north in the mid 90's is deffiantly an Eagles supporter, though would consider north as his 'second team'.