One of the main reasons why incestuous relations is illegal worldwide is because of the PROBABILITY that any children born from that relationship will have some form of physical disability and/or mental; disability.
This is the case for the brother and sister who you refer to. Two of their 4 children who were presumably born as a result of their relationship have disabilities.
There are parts o the world where incest is legal and a Search Engine search
I doubt it is likely that laws against incestuous relationships will be repealed in the near future and possibly never.
I personally think that this kind of relationship is terribly wrong and it is right that they remain illegal.
Loving a sibling or a mother or father is perfectly normal and natural but there is no need for this love to become a sexual one.
There are a few parts of the world where incest is legal and a Search Engine search will reveal them but even in some US States it is legal