1. BAM Reports are derived from Data Objects. And Data Objects are derived from any External Database Table, View or any component.
2. For your scenario, on Database side itself, I would recommend Create a VIEW that joins these 2 Tables and pull the required Columns and add required conditions. Verify the VIEW has all the rows expected.
3. Then create DataObject for this View. Once you have DataObject, create the Report. And for Report, you can have any Parameters also, that user can modify like Filters.