Ah I just can see trouble lies ahead, what
@ShionSinX write is what mostlikely to happen.
The problem is both of them is still have a feeling for each other, and that is what I see as a core of this problem.
Either one of them is move on, or both, or they end up together again.
The latter option is mostlikely to happen because, well manga logic, but at the same time most difficult I think.
Because the whole school(or classmate) already know they are sibling, (a not wise choice from the girl, well can't be helped actually cos they have a same name)
Will this manga focus on the "feeling" they have, or just play it as a standard romcom, though?