@Doobie_wop
Even if you had a hot sister, there is a good chance that you probably wouldn't be sexually attracted to her if you grew up with her (if she was a recently adopted sister or a biological sister that you only met recently, that's another story). Plenty of guys consider my sister to be hot but I never did. For most people, they tend not to develop sexual attraction to people they grew up with as children (there is a lot of literature on this but I'm too lazy to dig up the journals and what not. This is pretty well known anyway no?). There are exceptions to the rule but they are just that, exceptions. Just like how pedophiles (people who are attracted to pre-pubescent children) are exceptions to the rule.
Even if Nancy Botwin from Weeds (one of my favorite MILFs) was my mom, it's unlikely I would have developed a sexual attraction to even her even though she's probably the hottest forty-something babe I've ever seen. Because that instinctual incest aversion is so strong in our human nature.
