I noticed it in the game and quite honestly, I feel unaffected by it. Why most of you are all going "ew" is understandable considering the way you were raised and what culture you grew up in.
I'm rather open-minded and acceptable of these things. In Japan, you have incest mangas all over the place; Angel Sanctuary to name a bigger title. In that, it was a love (I mean love-love) between brother and sister which is much closer than between cousins. So it's more than likely socially acceptable in Japan.
Now, why didn't Square cut out or at least edit the fact that Brother loved Yuna? Wasn't America and the UK often the ones
whining about how the game can't come out fast enough for you?
Translation alone and voice acting takes a damn while. Add on that the mere thought of changing the cut scenes and the dialogue will waste even more of Square's precious time to devote to FFX-2 at that time or their future games. Also, I guess Japan just likes sharing its social culture with us.
I guess for most of you, anything outside your comfort zone or social norm must automatically be considered disgusting or gross. You have your right of opinion, and so do I.