To contextualize my question, I'm going to tell you what I'm not asking: Im not asking for proof of Ismah as a doctrine, but rather why Prophets have been given ismah in the context of predestination and free will. Moreover, I am not asking for proof of free will either.

My question is in multiple parts and I've done my best to break it down into yes/no type questions. okay, Bismillah.

Were Prophets chosen from the start or were they chosen conditional to whether someone in a society was capable of accepting Prophethood (by their own merit)?

If the former, then can't the objection be brought up that those prophets were essentially predestined heaven (and therefore making Allah unjust in some way)?

If the latter, then is it possible for ordinary people to reach the level of prophets?

If this is not possible and if what makes prophets better than ordinary humans the fact that Allah has granted them wahy and knowledge, then is it fair ask why ordinary people don't also receive that same treatment as mentioned by 12:24 which would thereby guarantee them heaven and protection from sin?

If the granting of wahy and knowledge is conditional upon someone having intelligence and purity, then is it a reasonable objection to say that intelligence is not a controllable factor?

If intelligence is not a controllable thing, then can the same objection be brought up that most intelligent people who are granted prophethood are guaranteed heaven (thus making Allah unjust again) because their uncontrollable faculty of reasoning was why they were granted wahy which prevents them from sin? (That is, someone's uncontrollable circumstances has led them to have a higher capacity, and therefore they have a greater opportunity to reach a higher level of heaven than ordinary people)

The Prophets are chosen based on the merits and their characteristics which Allah swt is aware of, so He swt knows in advance the characteristics thus chooses based on such. And since Allah swt has the knowledge of the future, so He swt chooses them to be Prophets AS before even their creation. Decision of Allah swt and His will does not bound to time, however, the execution of the decision is time bounded, like Mohammad SAWW was prophet SAWW in the will of Allah swt always, He swt chose to send him SAWW when he was born in this world.
The Prophets AS have choice to do good or bad, they are tested on their capacities, thus Almighty swt sets a proof and reason for the creation for his choice, their tests are on higher levels, such as if you would have done what Prophet Yunus AS had done , you would not have ended in the belly of the whale, it is Yunus AS who was tested in such instance and did not pass, though he was infallible from sins, he did not commit a sin per se, but his error was serious and it required him to get into isolation and training so such does not repeat.