Build the friendship first
Introduce the residents and keep helping them interact. Great Friends is a useful relationship target for a move-in request.
Watch for one Mii asking to live with another. Supporting the request is not enough on its own: the other resident must also agree.
Place the shared house
Once both residents agree, they ask for a larger home. The game opens Island Builder, where you choose a position for the merged house.
Dropping one Mii onto another resident’s home does not force a move-in. If the invitation is rejected, keep improving the friendship and wait for another request.
How many roommates can share?
A shared home can hold up to eight Miis. This is separate from the island’s 70-resident total.
Friends can be roommates without dating. A married pair may also ask to share a home, but cohabitation itself does not create romance.
Moving out again
Residents may later ask to move out alone or with someone else. A couple who marry while living in a larger household may want a home together. You can support the move or encourage them to stay when the request appears.
Do not plan a layout around being able to split any household immediately: moves are request-driven rather than a universal one-click eviction system.