Yes I understand how this question can go round in loops
With Allah there is no time. He created time. In His infinite knowledge He knew that these people (Prophets and Ahlulbayt) would be suitable to attain ismah. He does not need to create them to then see they’re good and grant them Ismah. He knew before creation.
Is this predetermination? Not really, since they have a choice and can sin if they wanted. In Quran a number of verses confirm this.
Therefore they’re the best people to receive this
Could we also have been those people? Possibly, but the choice was made for them. Why we don’t know. Some had to be chosen. Could we reach their ismah? Not their level but some level is possible.
The other thing to consider is some areas might confuse us more when we keep thinking about them, for eg what happened before creation of the universe, time etc..our intellect has not been created to take this information. Allah knows best