Yep, since a friend code goes off an induvidual 3DS console, and there are two consoles in your household, the two of you would indeed have two different friend codes. You're right that making multiple accounts is against the rules, but you should be glad to hear that that's not to stop the other person from making an account too. There are many people on ACC who have accounts sharing the same IP due to being brothers and sisters, parents and children, husbands and wives and so on! In fact, in your town Lantern which you have set up here on ACC, there's even an option for you to link other ACC members to it that use the town (found under this town's ACC Users). If you were to do that, the member who has been linked wouldn't even need to set up the town themselves.
If the other person wanted to make an account on ACC, that's by all means no problem, since they are a separate person from you. They could have a different friend code for their console (or the same one as yours if they want to play with yours) added to their account, and they could trade with other people independantly using their own character without any problems. I'd just make sure to use the same console that matching the friend code each time to avoid any confusion.
Hope I'm making sense!
PT me if you need help on ACC! :)
ACC +5! :3