If you have some photoshop skillz, just take a picture of all your villagers together with a black background, then delete the bg on your editing software and edit in a background of your choice. I've never done it but I'm guessing that's how you do it anyway lol. I love messing around with the amiibo camera when I'm bored though... like placing my villagers on random objects in my room
Just hold your finger over the camera so the background with be black, add all your villagers, take a picture, then take a picture of your mayor and photoshop them together!