Sorry, thats the trouble with work it gets in the way.
There are reasons why incest are illegal, and siblings marrying would be another kettle of fish, but i would suggest that somewhere, its happening.
I have no idea of the incidence of incest but I do know.
That straight people co-habit, That gay people co-habit
That straight people have sex, That gay people have sex
That straight people love each other, that gay people love each other.
That straight people can get married, that gay people can't get married.
That isn't fair, it isn't democratic.