They actually are, as a twin i can attest to that. Authors must be on crack or something because ain't no way we would do each other that dirty.
Here in my country we have a powerful family that had twins and they're on a fight to see who will be the one in charge. there's even a documentary and they both say in it that they hate each other since young age so I think it's not impossible that twins can hate each other to death.
That type of hatred is bred. It's something they were taught from a young age and I'm sure they don't hate each other to that extend, pride can often be confused with hatred. Maybe they just got big egos. But if they were raised normally then I dont think they would have ended up like that. But meh, ppl are weird species.
Why so many stories with identical twins betraying each other... I've always heard that in real life identical twins love each other to death