KHUX ► Questions about the beginning of KH X/Ux

[korr4k]

I have never played the games but, as a fan of the series, I still followed the story of KH X throughout its "three" games.

Giving it all a rewatch I have come across a couple of questions regarding the "beginning" of the story, if you could share your opinions on the matter I would be very happy to read them:

1. Does Ava have her proper union since the beginning of KH X which remains separate from the secret group of dandelions? During the KB war we see Ava arrive with several kids around her which I assumed are the ones under her union but not selected to become dandelions, am I correct?
2. After the war, the dandelions are brought to the Unchained realm and it is said that they are meant to re-experience their past life as KB wielder up to the point where the war takes place. How does this happen tho? It can't be just some kind of "illusion" happening in their mind to erase their previous memories because several clues imply the opposite, such as the fact that during their "sleep" they have nightmares about the events of the war. My question is then: who are the persons we interact with? I guess the dandelions could be the "real" ones, but what about the others that didn't come to the Unchained realm? I know my question may be confusing but let's make an actual example, let's say that after our first mission in KH X we meet "Maria", a proud member of the Unicorn, in the plaza. Maria isn't selected to become a dandelion and therefore dies during the war. When we re-live the event inside the Unchained realm who is the Maria we met? A "dream/projection"?
3. Along the lines of question no. 2, it is said that the events of Unchained X are the same as in X, diverging only near the war with the latter not taking place at all. To my understanding, it is at this point that the new 5 leaders make themself known and actually re-form the 5 unions as per instructions. Am I correct up to this point? If so, if the war doesn't happen, how it is explained to the dandelions that all the other guys and the foretellers disappear without the war taking place?
4. Why is Maleficent arriving at this point in time? Let's say that KH1 takes place in the year 100 while UX in 10, is there a reason why Maleficent didn't simply go back to her real world in the year 50 (assuming she was alive at this time)?