I think they really are fraternal twins. It would make sense since Hinata's father was a twin himself, and not to mention that they have similar hair styles (minus the bangs and hair color). I really do hope that they can at least activate the byakugan. It would be a shame to not be able to have that genetic power.
Naruto has wiskers because he was born and bred from the ninetails jinuchuriki while they still have kurama influence it's probably weaker because they where born in a non jin body.