No, they are not the same person. Sure, GENETICALLY they may be identical, but a person´s character is ALSO formed by his/her experiences. Of course these are NEVER exactly the same for each set of twins. Thus, they are two DIFFERENT persons.
And even if they were the same, would that really make it OK? Its STILL incest.
And even if they were the same, would that really make it OK? Its STILL incest.