Call Nintendo customer service. My old 3DS was accidently put through a wash cycle and had about 50 games on it. I called them and gave them my email address for NNID and serial number of new 3DS. They will tell you to wait a couple days for an email, and when you get the email you can sign into your Nintendo acct on the new 3DS and download all of your games. I only had 1 NNID, so not sure how it will work with 2, but hopefully they can accommodate.