Cousin-marriages are common in some cultures, and Japan is one of them. We've seen it in other shows as well, like SAO.
Problem is, their fathers are one-egged twins, so genetically they're half-siblings.. Maybe Kishi did not think of this.
But I both siblingship them and romanceship them. Not both at the same time, I'm fine with both but I can't choose my preference. x) I think both have been implied though, I really like them in the SD. <3´
I guess incest is quite a common thing in Narutoverse; at least in clans like Hyuuga and Uchiha.. I guess they like to keep their blood pure. I'd also like to know if there are marriages between members of different clans (aside from Hashi {senju} and Mito {uzumaki}). It seems like it's mostly either incest/marriages with people who don't belong to any clan (Minato and Kushina).
I wonder how ShikaIno, KibaHina, SasuKarin etc. kids would look like (dogs with byakugan, no? ) and what powers would they have.