one for each,
hari kiri for each

Nope... Just 2 fatalities... 1 4 noob + 1 4 smoke

I'm not sure about that. Someone's already posted a link to a bunch of Code Breaker codes (or Action Replay, can't remember which) that clearly lists two one-button fatality codes for both Noob and Smoke. Since only one of them has a fatality (that we've seen), I doubt that these codes would be for both fatalities. Why have two fatality codes for both Noob and Smoke if they only have two between them? Also, both Noob and Smoke have different animations for their Hara Kiri, although the button combo is the same.
So, here's my theory: Both Noob and Smoke have another fatality, that needs to be unlocked, and uses the button combo from the other's normal fatality to activate (Noob's second fatal uses Smoke's first fatal's button sequence to activate, etc.). You guys gotta remember, even using cheat programs, no one's unlocked absolutely EVERYTHING yet. I'm not saying that their second fatals are Super Unlockables, but the evidence that we've been provided does seem to indicate another fatal animation for both Noob and Smoke hidden in there, somewhere.

well if there are 2 seperate 1 button fatals for each noob and smoke with the cheat device...then why has no one posted OMG!!!! LOOOOOK!!!!! 2 NEW FATALS OH JESUS OH GOD LOOKKKKK!I FOUND ITITTTTT!
cuz you know the instant someone saw they had 2 each via a cheat device would know all over the boards.

i don't think so....it would be awesome if they have two fatalities separately but is very improbable in my opinion....and i'm losing faith for any "super secret" hidden in the game.
fear the Noob....

Noob has a fatality
smoke has a fatality and they share the same hari kari

Nope, Noob throws a bunch of shurikens into the air and they fall back down, stabbing him, while Smoke self destructs and explodes.