You can't be "inside" a decision
You have provided excellent examples of the problems with formal English and colloquial English. I've heard people use all of those six examples, all with the same meaning.
However, you can't be "inside" a decision. There is no definition of the word "in" that means "in consideration of" or "concerning." The closest definition is "to show a state or condition." (Merriam-Webster, preposition, kid's definition 5) But while similar, it's not the same thing.
Therefore, the more precise word to use is "about," meaning "with regard to" or "concerning." (Merriam-Webster, preposition, definition 4a)
Note that colloquially "in" and "about" are interchangeable in your examples. HOWEVER! They are not interchangeable generally. Therefore, the answer to your question, "is the use of in and about interchangeable?" is "no." My recommendation is that you habitually use "about" in those examples.