In sponge bob atlantis squarepantis do you need two ds cards to multiplayer?

You are correct! For multiplayer in SpongeBob's Atlantis SquarePantis, you need two DS cards.

This is because the game utilizes the "Download Play" feature. One DS card contains the game data, while the other DS card only needs to be blank. This allows two players to play together without needing a separate copy of the game on each DS.