Take a look into "Clean Architecture" by Bob Martin: https://8thlight.com/blog/uncle-bob/2012/08/13/the-clean-architecture.html
Just to summarize: your application's business rules must be testable without the database, the user interface, or any other external factor. Therefore, if your Entities expose stuff related to database, then perhaps your design could be improved.
My question is what object should the service layer work with? Should I return the Entities to my service layer methods for performing business logic calculations.
If your Entities are part of Repository layer, then they shouldn't be returned by your application (which is represented by your Services layer). Your application must work as one unit, and be testable too. So, define appropriate objects to be declared within Services layer and return them to whatever client might be using your app.