Inheritance on doctrine's embeddables
If you want to extend one embeddable from another you need to set the parents properties as protected not private.
If you want to use your Value Object in field then you should define new type in doctrine http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/cookbook/custom-mapping-types.html
If you want inherit properties from base then you should use @MappedSuperclass annotation http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/reference/inheritance-mapping.html
You should use @Embeddable when you want split entity by specific properties by creating specific entities. So you can't use Value Object as target. According to documentation (I'm not able to share third link).