well ill have to go take a look on that

but as far as im concerned the fourth isn't naruto but has a maybe the fourth soul sealed within him maybe wondering inside but unlikly the other two theory is that

naruto is A. his son

or naruto is B. his little brother

in the manga there is a statement by itachi uchiha that there after the yondaime isan and that can mean a few things like bro,brother,son, legacy so its a bit hard to figure out there relation