http://www.dailydot.com/irl/florida-man-granddaughter-marry-hoax/Fake. That website Florida Sun Post was registered just a few days ago.
And most states (if not all - I don't have the facts) have laws forbidding marriage and/or sex between two people as closely blood related as grandfather and granddaughter. I checked the Florida law and it states no marriage/sex between people of "lineal consanguinity" (and also extends the law to brother, sisters, niece, etc) which basically I interpret to mean if two people follow the same tree trunk straight up, they are against the law. Meaning these two Floridians would've been reported to authorities in the first place...if it wasn't fake.