Hey @trunktown ,
Unfortunately, Spotify operates on a per-user subscription model, so each Spotify premium account is really meant to be used by one person only (and one device at a time), so you can only stream from one device at a time. If you wanted to be able to stream in both rooms, you would have to have two separate Premium subscriptions.
A workaround, however, is to save your playlists to be availabe offline on your devices. Depending on the device you are using, there should be an "Available Offline" button in the playlist something. This will download those upbeat or peaceful tracks to the device, which you can then play freely by going into your device and entering Offline Mode (off the top of my head, in iPhone you can access this under Settings>Playback>Offline Mode. Now that device is offline and can play music saved offline simultaneously with the streaming device. Does that make sense? Hope this helps!