Wouldn't let them, don't think it's healthy.
First of all it's not all that uncommon for siblings to have a not completely equal relationship, even without parents knowing. Growing up together it's easy for one of them to take on a leading role where the other feels pressured to agree and follow, even if they feel uncomfortable about doing so. I don't see that as a good basis for a romantic relationship.
Next to that, should it go wrong where's the support structure? That's generally your family. If serious shit happens in their life, like major relationship problems, and they feel completely lost then I'd want for my kids, if I ever get any, to always be able to come home and feel safe and comfortable there. They can't do that if they're having relationship problems with their siblings, their parental home will never be a safe place for that.
The problems with incest don't stop at inbred children, that's quite minor as I see it. There's bigger issues with it, family relations just aren't suited for romantic relations. They're there for a very different purpose.
They can deny themselves for a bit, they're in puberty and will meet another wonderful guy or gal with whom they don't share such a defining past and with whom they can make a clean break in the future should things go wrong.
First of all it's not all that uncommon for siblings to have a not completely equal relationship, even without parents knowing. Growing up together it's easy for one of them to take on a leading role where the other feels pressured to agree and follow, even if they feel uncomfortable about doing so. I don't see that as a good basis for a romantic relationship.
Next to that, should it go wrong where's the support structure? That's generally your family. If serious shit happens in their life, like major relationship problems, and they feel completely lost then I'd want for my kids, if I ever get any, to always be able to come home and feel safe and comfortable there. They can't do that if they're having relationship problems with their siblings, their parental home will never be a safe place for that.
The problems with incest don't stop at inbred children, that's quite minor as I see it. There's bigger issues with it, family relations just aren't suited for romantic relations. They're there for a very different purpose.
They can deny themselves for a bit, they're in puberty and will meet another wonderful guy or gal with whom they don't share such a defining past and with whom they can make a clean break in the future should things go wrong.