Okay, amending the previous statement .

Those are off-limits for everyone but Atem. I know it says all cards a free use in the decks you have your characters use, but this is also anime-based. And, in the anime, the only person (or people) who owned all three god cards ultimately were Yugi and Atem (aka, Yami).

The Sacred Beasts, however, you can put in a character's deck. Just make sure that the rest of us know ahead of time; there's only one copy of all the sacred beast cards in the anime.