Learn English – Is “forth and back” more proper than “back and forth”

I'm having a lot of trouble seeing the problem here. The fact that you are using a verb of identity makes no difference, except to allow for another acceptable way of phrasing the sentences. (And by the way, you could construct similar reversals even in the case of transitive verbs, if you wanted to, by using the passive voice, thus: "Koalas are liked by whom?" I wouldn't recommend it, and it's a bit unusual, but it's perfectly grammatical.)

As for the specific example (the "who our boss is going to be" vs. "who is going to be our boss" problem), each version is perfectly fine, perfectly grammatical, and perfectly acceptable. They are equivalent, and each is correct.

In your examples, 1.a is correct because it is referring to what the subject, or person, is current hearing. it is still in progress. 1.b would mean the same thing as " I can't believe what I am able to hear from here". It does not refer to what you have heard, instead it refers to what is possible to hear.

2.b is more natural and you are correct in that scenario. What you should consider is that since it is a movie, they may have only shown the character witness the dark entity once but still could have seen it after as well.

In example 3, both are correct but differ in meaning. 3.a means that the subject is still seeing it. Also, it could be referring to something specific. With 3.b, it is more open ended so the question could be general, as in nothing specific.

example 4 seemed to have been well answered in the other forums. I hope this was a little helpful.