As for the third, that's simply not what happened in the movie, as has been mentioned several times. Whatever you want to believe about the rest, the Ancient One is *crystal* clear about the Infinity Stones and their effect on time. Removing any stone from the timeline creates a branch timeline. Thanos and his army traveled forward after the Avengers removed the Power stone, so they never came from the original timeline at all. And once the power stone was returned, that branch timeline was prevented from ever existing in the first place, so no one would ever miss them.