Happy Home Designer doesn't need amiibo cards to play properly, you get random villagers as you progress. Amiibo cards are just for if you want specific villagers right then and there.
Amiibo Festival only requires one amiibo to play, and it's bundled with two, as well as three amiibo cards. All players without amiibo are allowed to play as villagers.
In the two amiibo games they have, the extra amiibo are optional and not necessary to play the game.