Question

Have a good week! 
1- If I understand correctly (?), logical empiricism adds to what Hume and Locke said not only that the concepts of thought are built through observation and are not innate a priori in a person, and accordingly Hume argued that we have never encountered concepts like “infinity,” “causality,” “God,” etc.; rather, it also claims that metaphysics and such concepts have no cognitive meaning at all and are nonsense.
That is, whereas for Hume they indeed have no objective value and do not exist in reality, the Vienna Circle adds that they do not say anything even to the person?
2- I do not understand where their assumption comes from that a concept whose representing word does not point to an observable referent has no meaning (and is somewhat like a private language). Maybe they are right that concepts that cannot be examined empirically do not exist, but why should they have no cognitive content?
3- According to the positivists, it follows that a scientific theory cannot describe theoretical entities that are not observed, as Mach (the father of the positivists) indeed held: that scientific theory never assumes there are objective entities, but is only a convenient and practical way of relating to reality, whereas every case in nature is only a particular case and nothing more.
If so, it is difficult for me how one can speak at all, for example, about the principle of causality, which is not observed. Hume indeed argued that it does not reflect reality but the human being, but according to Carnap would we have to say that causality is nonsense?
That is, how can Mach claim that theories are only a convenient way, if it follows that one cannot speak about them at all and they are nonsense? And how can one relate to them at all even if they do not reflect reality itself?
4- How, according to them, can one speak at all about concepts such as “ownership”? Or even, how can one relate to a group of items as one thing? After all, the way to connect items such as triangles to one another and define them as the form of a triangle is either by Plato, who sees the Idea of the triangle, or by Aristotle, who argues that this is only an abstraction carried out in thought. If so, how can one relate to a generalization of things, given that the generalization itself is not empirically observed but is personal (at least according to Aristotle, and certainly not according to Plato)? If so, one cannot point to it.
Likewise, how can one describe psychological theories and even any social situation, given that one cannot point to the general definition itself?
5- Mainly, why do they claim that scientific entities have more cognitive value, even though they are only a convenient way of relating to reality and are not observed, than God does? After all, insofar as one can refer to and use the principle of causality, etc., even though they are not observed and are only for convenience, likewise we should be able to refer to, use, and speak about God as well (even if He does not necessarily exist and is not observed, at least as a calculation/model), since the concept of God is a convenient way to build a theory about the world insofar as it explains its existence. And just as the principle of causality is not nonsense even though, according to them, it does not exist, at any rate one can use this concept?
6- How, according to them, does science operate at all? What does it mean that there is a particular case and we do not really see the entities? How do they compare things to one another and build a general law?
Thank you very much!