Your second question has a general answer. Most languages use tones, which means tones change in the course of a sentence. If the tone changes for all sentences, then it also changes for questions. I know that’s not what you were trying to ask, but that’s the answer to the question you did ask.
If you need a way to indicate that something is a question, you could do what English does… You could use question words at the beginning of the sentence. You could change word order. You could add extra words… Which is to say, you’re not dependent on intonation, though you could use it if you want to.
If it’s an official act, yes. It’s not hard to tell a story where it becomes an official act. I I think he could still be impeached FWIW.
Because of Trump’s unhinged tactics, we know that top military leaders and (presumably) TLA bigwigs have discussed what they would do in situations like this. What you’re describing is very close to a coup d’etat, and in a situation where they get ordered to perform such an action, do they do it? What was framed as a question of SCOTUS rulings becomes, in reality, the question, “Am I willing to throw this entire democracy away on this President’s absurd orders?” Every high-up in government knows this… They signed up to serve the people, not a dictator.
Of course we have no idea how each person would act, but my point is that pure legality is only one challenge Biden would have to overcome if he wanted to do such a (horrible) thing.