How to retrieve Customer, Cusomter Account, Customer Account Site CBO through apps composer page

Summary: We are in process of building a Custom Business Object through application composer to achieve certain functionality in Order management. In the CBO, we have three feilds Customer, Cusomter Account, Cusomter Site. Once a customer is selected customer account should display the accounts related to the customer selected. Once customer account is selected then cusomter site should display sites that belong to only that particular customer account. Please help to know which standard objects can be used or suggest other option to achieve above. 

Content (required): We are in process of building a Custom Business Object through application composer. In the CBO, we have three feilds Customer, Cusomter Account, Cusomter Site. Once a customer is selected customer account should display the accounts related to the customer selected. Once customer account is selected then cusomter site should display sites that belong to only that particular customer account. Please help to know which standard objects can be used or suggest other option to achieve above. All three fields are created as Dynamic choice List. We are able to achieve Customer and Customer site as expected by