Music Membership

My husband and I have family sharing. We have his iPhone, my iPhone & iPad, and our oldest iPhone all linked to family sharing. We never had an issue, until now. My husband purchased an iPad Pro for himself, and we are having troubles to have both his iPhone & iPad linking to the family share. I don't see anywhere say limits devices. I had seen it’s limited 6 family members, but not devices. Every time he takes himself off family sharing & re-adds, the iPad would work until he uses his iPhone. It's not allowing family sharing music on both his iPhone 6 plus & iPad Pro.