Well, if people discern, while being accompanied by a pastor or lay pastoral worker that, in conscience, an irregular union between immediate family members is the best they can do in the concrete circumstances of their complex situation, who are we to deny Communion to a brother and sister living as husband and wife if they sincerely want to change their situation? They might need to continue their relationship...you know, for the kids. All such situations are unique. We can't pigeonhole or engage in overly rigid classifications. Rule books are so yesterday!