I feel sorry about them but not in the way you mentioned. I have a friend who's sister was like Courtney Cox from Friends, Season 1. Yes - that damn good looking. But it bothered him because, well, it's weird when all the creepy guys in the entire shopping mall are staring at your own sister. This was weird when we were 15 and she was 18.
The "man, the two hottest girls in the school and he is not allowed to be attracted to either of them." angle never, ever features in. You really have to have a sister to understand that. There are enough attractive women out there - not staring at your cousins and sisters isn't as difficult as you think.