Hello Nandish,
Since you don't want to use $select,
In that case i suggest to create two different entities.
One for Self and another for Dependent and maintain the only required properties for both of them separately.
Implement methods for above entities separately and fire the service by passing particular entity on selection in the UI.
In this way you will get fields which are required for self and for dependent based on selection in the UI level.
Regards,
Ashwin