In the United States, every state and the District of Columbia have some form of codified incest prohibition.[18] However, individual statutes vary widely. Rhode Island repealed its criminal incest statute in 1989[18], Ohio only targets parental figures[18], and New Jersey does not apply any penalties when both parties are 18 years of age or older.[18] Massachusetts issues a penalty of up to 20 years' imprisonment for those engaging in sexual activities with relatives closer than first cousins[18] and Hawaii up to 5 years in jail for "sexual penetration" with certain blood relatives and in-laws.[18]
In all states, close blood-relatives that fall under the incest statutes include father, mother, grandfather, grandmother, brother, sister, aunt, uncle, niece, nephew, and in some states, first cousins. Many states also apply incest laws to non-blood relations including stepparents, step-siblings, and in-laws.[19]
So.. Yeah. Special stuff there.
Though they don't say much about what they've done so far (oh darn /s), but they're getting this done through a surrogate. So technically, the baby will have the grandson as the father, and some random woman as the mother - at least literally. As for the relationship in general, WTH. I mean, I guess its at least good to hear that they didn't grow up living with eachother and then this happened, but the fact that they're related is just weird.
Not sure how it applies, but I'm pretty sure they'll not be able to go to certain states, at least not with eachother. Incest is incest wherever you go, and the laws of that state / country will probably take precedent over your home state.