It's already too late, but have you considered hacking the original new super mario bros in order to make entirely new levels ?
It could be legally distributed as an IPS patch, and you would already have the graphics, the music and the engine and great gameplay from the original New Super Mario Bros for DS.
You guys would only have to create the levels!, and putting all the effort into the levels would most likely result in an awesome new game!
level editor: (have not tried it yet, linux user)
http://www.romhacking.net/utils/457/
It could be legally distributed as an IPS patch, and you would already have the graphics, the music and the engine and great gameplay from the original New Super Mario Bros for DS.
You guys would only have to create the levels!, and putting all the effort into the levels would most likely result in an awesome new game!
level editor: (have not tried it yet, linux user)
http://www.romhacking.net/utils/457/