Let's say you plan to buy the game for your entire household and share a single copy with a partner or kids. Like in previous Animal Crossing games, this means all residents become individual characters in a village, and they each get their own house and their own progression track (particularly in paying off Tom Nook's loans for an expanded house). There is no way to create multiple islands on a single console, should people prefer to have a village to themselves. Each new island requires buying an additional copy of the game and an additional Switch, due to how Nintendo has structured AC:NH's save files.
Maybe that structure is fine by you and your likely Switch-sharing posse. Like in older games, this sharing style promotes some cute moments, including the ability to leave surprises on neighbors' virtual front lawns or have the game's non-player characters (NPCs) refer to your real-life friends in conversation. If so, you should still be warned that only one of your island's residents will be treated as a first-class citizen.
Whoever turns the game on first is dubbed the "Resident Representative." Tom Nook immediately puts most of the island's progress on their shoulders. A few early, tutorial-like missions, including building the island's first store and welcoming the island's first new additional residents, can only be accessed by this person. Logically, that makes a certain sense, since all players are able to affect the island. Why would Tom Nook ask each player to build the island's "first" general goods store? But Nintendo didn't come up with alternative island-building ventures for each additional resident who moves in.
Worse, only the Resident Representative can build some of the biggest updates for each island, from a new series of bridges and incline ramps (designed to let players move more quickly through the series' largest villages yet) to sillier customizations like the town's flag and song. If you'd like to contribute to any of this stuff or any of the quirky village-building missions (particularly an early mission that revolves around inviting a "celebrity" to your island), secondary players will have to coordinate in real life with the Resident Representative.
