Well first suggestion is not to extend controllers for this and instead extend the services but this one falls wayyyyyyyyyyyyyyyyyy outside “normal usage” and honestly I wouldn’t really advise what your doing (as you can already tell the complexity of this is mildly frustrating at a minimum).
If you don’t mind me asking, why are you duplicating this in two isolated databases? Whatever “pulls” from that other database, why not just have it call Strapi’s REST API instead? (That is kinda the point of a headless cms 
)