@GooglePlayMusic If someone pays for a family plan they shouldn't get messages like "It looks like you're playing music on more than once device" should they? That's why I paid extra, or so I thought.
Hi Matt, you can use multiple devices with one account, but one of those devices can stream music at a time. Since you have a family plan, you can use one of your family member's accounts on your other device to stream music simultaneously. Let us know if you have questions.