C
Is it possible to convert the retro games like Double Dragon for the NES to a NDS game?
S
No, you'll need a NES emulator for the DS, it will then be able to play the NES games. I don't personally know the names of any NES emulators but I'm sure someone will know.
A
Use NesterDS, or NesDS. See this https://www.romulation.org/forum/index.php/topic,5002.0.html