Welcome to the FusionAuth community!
It isn't possible to create new tables inside FusionAuth. However, you have a few options within the current supported extension points.
You can correlate between two different databases, as you currently are. You can use the user.data and user.registration.data fields. These are arbitrary JSON objects and you can define your own schema inside them. They are searchable. You can use Entity Management. Entity Management lets you define your own entities (which also have data fields) and relationships between users and entities. This is paid functionality that requires a license key.Hope that helps.
Dan