Get the Multi Room Music Starter Kit | Echo (4th Gen) and 2 Echo Dots (4th Gen) ($110, originally $200) and use Alexa in multiple rooms.
You can use Alexa and multiple Echo Devices as a household intercomm system, by simply saying "Alexa, drop in on Master Bedroom" or "Alexa, announce..."
To play music, podcasts, or audio books in multiple rooms, simply say "Alexa, play Today's Hits on Apple Music everywhere" or "Alexa, play An Oral History of The Office podcast on Spotify everywhere." To play audio in a specific room, just say "Alexa, ask Sleep Sounds to play Rain in the bedrooms."