Well, the Welcome Amiibo villagers (such as Ketchup, Julia, Dobie, etc) basically function as normal villagers and can be adopted normally as well so you don't require their cards. As for the Sanrio ones, only the card holder can adopt them. Even if they are in boxes you just won't get the option to adopt them >~< (That's why I bought my Sanrio cards, I really wanted Étoile in my town! So sparkly!)