Thank you for your post.
Relationships in FileMaker Pro are created using a "key" or matching field. With Bento, the relationship is manually created. That is, there is no "key" field or matching field. Therefore, the link provided by "Jade" (Thank you for the example!) is a good starting point. This would allow you to assign a "key" field to the records, and then import the libraries into tables, and then link (set a relationship) between the two tables/libraries via the "key" field.