...

nvm I think it is.

Not really... it depends on how you persive it... her mother married their father, so she is their sister by marriage but not blood... So it should be classified as non-blood related incest...

I mean she still calls them her brothers which is still weird.. if they are brothers to her that's basically incest. I mean if they arent blood related at least they wont have deformed kids!

I don't think so. She wasn't born into the family her mom married into it so for three boys to suddenly have a sister its no wonder they never saw her as a sister. Expectantly the oldest he was taking care of them as a father would so even more so he doesn't see her as a sister. Its not as rare as you think for step siblings to get romantic feelings for each other